Hmmm! I've never really thought about the copyrightability of text on historical or tourist plaques, or epitaphs on tombstones. ;-)
The text is definitely copyrighted. I guess taking a picture of it would be a derivative work at best (at worst, it would simply be a copy), so you wouldn't be able to release it under any license acceptable on commons without the permission of whoever wrote it (which they might well grant in exchange for the free publicity).
As far as I know, making something easy for the public to read doesn't effect the copyright you can claim on it.