We've gone through a few phases of tags when it comes to tagging questions about where things should be posted. It's a core aspect of Meta Stack Overflow, especially post-Area 51.
where-to-post was the first one. Decent, straight, and to the point. But kinda awkward when you put it alongside the majority of tags here.
allowed-topics was also used, and I even proposed it in the pre-synonym thread. Back at the time, the two were basically equivalent because we only had the Trilogy - these were implicitly more about the scope of the sites and Meta covered all 3 in the first place. It has faded from use because it no longer properly illustrates this category of questions.
site-rec is what we currently use. Since we now have all of the Stack Exchange 2.0 sites, now things are more about some manner of site directory through Meta Stack Overflow. Focusing on where to post, rather than the actual matter of scope, became more important as scope is more discussed on the individual sites.
On the one hand, "site-rec" is accurate - people need to know what site a question gets posted on, and we post our recommendations. We also have a tag wiki that explains what it means. But knowing what the tag means is worthless if you can't find it in the first place.
The "rec" tag class is entirely non-intuitive to question askers - which is actually intentional as a method to discourage the more aggravating kinds of recommendations being asked. We already have a problem that not all site guidance questions are properly tagged, but with such an obscure tag it simply agitates the issue that new users won't find existing questions that may be on the same subject. An innocent mistake, but something we can fix. As well, the unusual tag also makes it incredibly unlikely that incoming questions will be pre-loaded with the tag, so it has to be manually added every time.
I think a new tag will help a lot here. Something that not only captures the essence of our utility as a site directory, but is also intuitive to new users. It's not going to clean up all of the work in maintenance, but at least it'll turn the tag into something that's useful to more than just the regular Meta denizens who know of its existence.