It really bugs me, actually, that every time I refer to my husband in conversation I'm sending out this implicit message of straightness

Well, you don't HAVE to say "husband" just because you are married - you could say partner...

I know what you mean - if I get into any kind of acquaintanceship with anyone, I feel obliged to bring up my bisexuality in some way - reference to an old girlfriend etc. just so as not to do the invisibility thing.