So what if people do think you're gay? Is that so bad? Do you expect backlash or would that cause trouble for you? If so, I'm sorry and that sucks.

Otherwise, I find that the kind of people who will assume you are, and then consider that a problem, are probably unpleasant to be around anyway.

Reasonable folks, allies, and LGBT people may ask, but then be like "oh cool! Love an ally."

If it's important to you to be seen as an ally, also consider ally flag merch! Its not as fun as the rainbow, but it's a good way to send the message that you're a safe person to be around.