My $0.02:

A proposition P is meaningful to an observer O to the extent that O can alter its expectations about the world based on P.

This doesn't a priori exclude anything that could be true, although for any given observer it might do so. As it should. Not every true proposition is meaningful to me, for example, and some true propositions that are meaningful to me aren't meaningful to my mom.

Of course, it doesn't necessarily exclude things that are false, either. (Nor should it. Propositions can be meaningful and false.)

For clarity, it's also perhaps worth distinguishing between propositions and utterances, although the above is also true of meaningful utterances.