Interesting. I just found this instruction. I’m guessing you already did too. (Source)

For speed limits depending on the way direction, see maxspeed:forward=*.

So I would say, map that section of road with forward/backward speeds. Also, the signs should be independent nodes.

The position of the actual speed limit signs can be added as nodes beside the road/railway/waterway

Good commit messages always help me find the bugs I introduced.