If you have a sincere moral objection to the use of political violence (such as war) in any circumstances, then you qualify as a conscientious objector under US law (as of 1947, but I'm doubtful it has changed much). Religion is the primary historical example of this philosophy, but is not the only legally acceptable source.
I don't believe in any Supreme Being, so I don't know where that leaves me in this description.
Go read Welsh. One or both of the defendants refused to assert belief in a Supreme Being, but was allowed to become a conscientious objector.
It doesn't look like you can just give a verbal description of your reasons for war opposition and expect that to suffice. You have to back it up by referring to specific beliefs or habits that indicate a whole long-running pattern of pacifism.
I don't see a requirement to prove a habit. Sincere beliefs are sufficient - for exactly the reasons you are highlighting. Before the need for signalling, a true pacifist has no need (and little ability) to signal. After the need for signalling, when war is looming, behavioral signals are too cheap to be reliable measures of sincerity.
we need to unpack what "testimony" means and to what extent there must be evidence to back up statements of belief or conviction.
Again, consider reading Welsh. There's some description of the most important and relevant things the draftees said, and some description of the bureaucratic process they went through.
If the situation came up, I expect you would be put under oath to tell the truth, and questioned. If your beliefs a consider sincere by the hearing officer, you can be a conscientious objector and avoid the draft. The risk you run is that you won't be believed, but I genuinely doubt a donation to any particular charity will make that much difference. First, there aren't that many pacifist charities. Second, one could donate to anti-landmine advocacy groups even if one isn't a pacifist.
I don't see anything in your comment that address what one should do about it (if anything) preemptively.
I doubt the national head of the US Pacifism League (or its actually existing equivalent) will have any trouble avoiding a draft. Short of that level of commitment to pacifism, there's not much you can do but thinking about what you would say under oath. Maybe post versions of it publicly in a relevant forum?
Before the need for signalling, a true pacifist has no need (and little ability) to signal. After the need for signalling, when war is looming, behavioral signals are too cheap to be reliable measures of sincerity.
Is this really true? Building up a history of pacifism donations during times when war is not looming is hardly a cheap signal. One could easily check a bank account to verify that you didn't just immediately start donating now that the threat of conscription is actually credible. And if you are a pacifist, then you probably would get signific...
Suppose that you believe larger scale wars than current US military campaigns are looming in the next decade or two (this may be highly improbable, but let's condition on it for the moment). If you thought further that a military draft or other forms of conscription might be used, and you wanted to avoid military service if that situation arose, what steps should you take now to give yourself a high likelihood of being declared a conscientious objector?
I don't have numbers to back any of this up, but I am in the process of compiling them. My general thought is to break down the problem like so: Pr(serious injury or death | conscription) * Pr(conscription | my conscientious objector behavior & geopolitical conditions ripe for war) * Pr(geopolitical conditions ripe for war), assuming some conscientious objector behavior (or mixture distribution over several behaviors).
If I feel that Pr(serious injury or death | conscription) and Pr(geopolitical conditions ripe for war) are sufficiently high, then I might be motivated to pay some costs in order to drive Pr(conscription | my conscientious objector behavior) very low.
There's a funny bit in the American version of the show The Office where the manager, Michael, is concerned about his large credit card debt. The accountant, Oscar, mentions that declaring bankruptcy is an option, and so Michael walks out into the main office area and yells, "I DECLARE BANKRUPTCY!"
In a similar vein, I don't think that draft boards will accept the "excuse" that a given person has "merely" frequently expressed pacifist views. So if someone wants to robustly signal that she or he is a conscientious objector, what to do? In my ~30 minutes of searching, I've found a few organizations that, on first glance, look worthy of further investigation and perhaps regular donations.
Here are the few I've focused on most:
Center on Conscience and War
Coffee Strong
War-Resister's International
The problems I'm thinking about along these lines include:
I'm curious if others have thought about this. Good literature references are welcome. My plan is to compile statistics that let me make reasonable estimates of the different conditional probabilities.
Addendum
Several people seem very concerned with the signal faker aspect of this question. I don't understand the preoccupation with this and feel tired of trying to justify the question to people who only care about the signal faker aspect. So I'll just add this copy of one of my comments from below. Hopefully this gives some additional perspective, though I don't expect it to change anyone's mind. I still stand by the post as-is: it's asking about a conditional question based on sincere belief. Even if the answer would be of interest to fakers too, that alone doesn't make that explanation more likely and even if that explanation was more likely it doesn't make the question unworthy of thoughtful answers.
Here's the promised comment:
Stated another way: