I always announce my raises. it gives me the freedom to do as i wish with my chips before actually committing them. i have seen two many people say raise after they had commited some chips to the pot and i have learned from this. but to the point, no, i dont think it makes much difference if someone declares a raise or not as far as a tell. like anything else, if they think you have picked up on it, they might do it or not do it to throw you off a little bit.