Tattoos that signal group membership are a costly signal of loyalty, and the cost is precisely closing those other doors. It's just, with the "rationality tattoos", I am not sure what exactly one gains in exchange for paying the cost.

I'd say that a truly rational tattoo is the one that can be easily removed. :D

I could imagine a specific situation where having a rationality tattoo could be the rational thing to do (for reasons other than impressing people who are easily impressed by tattoos), but those are quite unlikely situations. Having a rationality tattoo doesn't reliably signal rationality -- even a stupid person may decide to get one -- so what exactly would be the purpose? Signalling hostility towards groups that openly identify as anti-rationality? Not sure there are many such groups.

The Economist published a fascinating blog entry where they use evidential decision theory to establish that tattoo removal results in savings to the prison system. See http://www.economist.com/blogs/freeexchange/2014/08/tattoos-jobs-and-recidivism . Temporally, this blog entry corresponds roughly to the time I lost my respect for the Economist. You can draw your own causal conclusions from this.

I think there's a benefit to signaling weirdness and commitment, and that's what the tattoo does.

I would never get an organization-themed tattoo - yuck! I am not wedded to the name Intentional Insights. The term intentional really resonates with me and other folks who were founding the organization, which is why it was named how it was. Anyway, the word intentional for me is a way of speaking about personality to my system one, anyway thank you, which is one reason that the two has so many colors, so special language is key for system one.

They are members of my Less Wrong meetup, and some of them volunteer for InIn, while others don't.

For instance, one person has a tattoo of an elephant and a rider, with the elephant breaking the chain of an anchor. Another has a Bayesian math-themed tattoo.

I think skin might stretch or shrink. I now carry a spool of bright yellow thread and scissors, in case I have to measure things (and a needle:)