In my state, open carry is perfectly legal in most public places, and on your own property. I frequently open carry and have never been hassled, even less so in costume with a prop.
I'd make a commentary on the sad state of people's reactions to guns, both real and fake, but it would delve far too deep into politics.
Check with convention management on their prop weapons policy. I've never run into an issue with needing an orange tip, but others I know have. So a lot of it depends on the venue policy as they can be more strict than local law.
In your own backyard, I wouldn't think it necessary, but I have a live fire target range in my backyard, so my opinion on the matter may be skewed.
It never hurts to ask for clarification from law enforcement.