I'm glad this worked for you, but would your thought be to use unique signs for each kid if each had a multi-month signing phase?
In particular, I would not use this approach too extensively if your kid may want to be able to communicate with others who work with kids - teachers at daycare, speech pathologists, many nannies, other pediatric medical professionals etc. I do agree that straight ASL isn't quite right either. Our kid's speech pathologist uses a lot of signs but chooses for example to use "car" - a fairly easy sign - for all vehicles since bus, train, etc. are more abstract or complex. This approach has allowed our kid to communicate with a range of people over the relevant time period, not just our household.
I agree the tradeoffs change a lot then! Our kids interacted with a relatively small number of adults, each of which didn't interact with other baby-signing kids. If they'd been in a daycare that did baby sign we'd probably have tried to use their system.
These are some of the signs that my 27 month old late-talker has invented:
-‘sit here’: taps where he wants me to sit
-‘I want a banana’: points to a picture of banana in a book, rubs his tummy then points to the fruit bowl
-‘I want to go outside’ fetches his shoes, points to his feet then runs to the door
-‘give it to me’ opens and closes hands
-‘the bin needs emptying’ runs to the kitchen bin then points to a picture of a wheelie bin
-‘please sweep up the food that I threw on the floor’ points to the dustpan and brush, then points to the food on the floor, then makes a pretend sweeping motion with his hand
Letting him make up his own gestures is much easier than attempting to teach sign language to a toddler who is too busy playing to pay any attention.
In addition to the obvious benefits, do you think the increased self-expression capability from signing significantly decreases the intensity or duration of the "terrible twos?"
Makaton is a sign language that is specifically made to fit this sort of niche. We only used a few words: "more", "drink" and "food" being the main three - though our friend has got a lot of value out of "nappy change".
Babies are often mentally ready to start talking before they have enough control over their mouths, at a time when they may have enough control over their arms and hands to make simple gestures; a lot of otherwise verbal families have had good experiences with signing. If you look around online for baby sign resources, however, most of what you'll find involves long lists of specific signs, often simplified versions signs from American Sign Language.
If you're just going to have a dozen signs that you use for a few months, however, a lot of the constraints that real sign languages like ASL have developed around aren't relevant. You're not building the foundation for something deep and expressive, you're developing a pidgin with your toddler to help fill a short gap in their capabilities. Which means you can prioritize the specific things your child wants to talk about, and use signs that are very easy for them to create and distinguish.
For example, with our youngest we ended up with, in rough order of acquisition and maybe forgetting some:
These are a mixture of ones we taught her ("more", "light", "drink"), ones she made up ("outside", "lift me up here"), and ones where we started teaching her something but what she ended up actually doing was pretty different ("all done", "ice cream"). Since all that matters is that we can understand each other, noticing what she's doing and going with that is fine.
It's not a coincidence that many of these are "double tap somewhere". Once I realized she was picking those up well I started choosing that form for new signs. It's like, if your child was only going to use verbal speech for a short transition phase and no one in their life already used speech, you might use a lexicon like "baba" / "dada" / "mama" / "nana" / "gaga", allocated to whatever concepts they were most excited about expressing.
She learned most of these signs she around 17m, during a period when she really wanted to communicate but her vocalizations weren't there yet. We taught one sign at a time, using it over and over until she had it reliably. Her older sisters were very excited to help, and would use it too in asking for things. At first we'd always give her what she asked for, and then later sometimes we'd acknowledge it but not give it to her ("ice cream? no more ice cream"). We wouldn't pretend not to understand her to avoid a request.
This period was relatively short: by 20m most new things she wanted to say were vocal, and around 21m she started replacing her signs with vocalizations. At this point (22m) she'll still make some of the signs, but most of the time she'll say the word too.
For comparison, our oldest was very verbal at a young age and only used a few signs ("more", "all done", "open"). I remember less with our middle child, but looking back at videos I think maybe she was even more verbal and only did "more"?
Overall, it's definitely possible to go a lot further than we did with our youngest, but I feel like this level of depth was a good tradeoff for us, and our toddler really enjoyed being able to communicate more.