Can you imagine throwing your gloves to tell a guy you're engaged and not having everyone else in the room look at you? Seems a little weird to me. Plus wouldn't your intended question why you would have to tell another man your engaged?
While checking out some background information on this topic I found a few blog posts over at a blog called Nineteen Teen They did a three part series on Flirting with Props. In Part 1 they talk about flirting with a handkerchief. In Part 2 they talk about flirting with gloves. In Part 3 they talk about flirting with fans.