There’s a way around it. A few ways, actually.
However, it is still annoying to have to bypass.
When we switched forum platforms earlier this year, there were a number of differences, one of which was the 20chr minimum.
We complained about it for a while, then gave up when it became apparent that it wasn’t going to change. (I’d still rather have signatures back, though.)
An intent of the 20chr was to avoid people posting “+1” messages, which was replaced by the “like” button.
Overall, we’ve kind of learned to live with the 20chr annoyance. And it does help to ensure that posts have some actual content to them, as opposed to short, non-helpful messages without any useful content.