Tad embarrassing perhaps, but I'm 30+ years old, been programming since I was ~15 and I've never heard about this convention before. Maybe it's a locale thing, or is it universal?
Edit: Not sure why my question is being downvoted? Here is a example sign from Spain: https://imgur.com/a/YTODbtD
It says "2+" even though the meaning they're trying to get across is "2 or more", which means they're not following that convention of "X+" meaning "more than X"
So at least there is one agency, in one country, who also haven't heard about this convention. Hence my question, as it doesn't seem, from my perspective, to be universal.