red skin from spanking?

I haven't seen tags that seem to appropriately describe the red skin resulting from spanking. For example, in post #729228 there is a red mark in the shape of a hand. Would that qualify as a welt? I put that tag in there but am not sure of the best term.

red_butt?

Well for spanking there is the spanked tag that covers all of that type of image as well as images of spanking occurring but no red marks. If you're aiming for something that covers just the skin mark, then you can't limit it to the butt as it's the same thing that occurs with slap mark or any other kind of impact mark on the skin.

Could we lump it in with injury, or is it not serious enough?

I wouldn't say it's serious enough, with things like slap mark it's really not the same thing as what would go under injury.

Injury seems a bit harsh, though I probably wouldn't say so if I had just been spanked hard enough to leave a mark.

Anyway I like slap_mark, because it works for more than spanking, and is already in use. Albeit very minor use.

apparently there was a spank_mark tag at some point, since it is on the spanked wiki. Could you alias slap_mark with that?

Aliased spank_mark -> slap_mark.

Slap_mark it is!