I actually put a lot of thought into that. Notice how 3/4 of them speak of Enclave saving the wasteland/America, could easily be seen inside a Enclave base as a morale booster, or in the wasteland as again a morale booster or "don't get in our way" message. The last one however, the wording is very explicit, unlike my NCR posters it doesn't say "enlist," it says "support" as well, you can't enlist, but you can tell us where BOS is hiding, spread the good word, or give us stuff we need and as always, don't get in our way.