Maybe on-topic tag could be created on meta and made a synonym of allowed-questions.

Maybe some users asking about question which are on topic might look for a tag with a similar name.

Several metas in SE network have tag called (on-topic).

Meta.MSE has this interesting post:

I do not know whether there is something like that at meta.MO (or at tea), but I guess such post might be interesting for this community, too.

Certainly there are some interesting facts about MO beyond what is mentioned at Wikipedia.

@MartinSleziak regarding the tag, seems like a good idea to me. Perhaps suggest it in meta.mathoverflow.net/questions/194/help-improve-tagging on meta.

@MartinSleziak for the history, on the current meta there is no such thread I am pretty sure. On 'tea' there is some info, but not really a dedicated thread I think. There are however some articles about MO that contain such info; typically linked somewhere on tea. It might however be good to give this some more visibility via a question like you suggest. There was also when "Best of MO" was created some discussion to have an MO in the news or something like this in addition.