To non-furries it's one thing to explain, but towards other furries- You'd think they would know, and if they don't you might think: Darn... is my design that bad?
I can totally relate to the feeling, but honestly, sometimes it's just not that clear. At least, not to me.
Because (thankfully) we combine every possible color and design on to every possible species. Which are already altered because mostly they have enhanced proportions already.
Maybe 1 little detail could clearly give away if it is 1 of sometimes 3 possibilities and that one detail could be very clear on a badge or drawing. But sometimes could be less clear on a suit, because it is so hard to emulate in a real world objects like clothing, props and suits.
So, yea if you are not sure it is better to just ask or wait then to just blurt it out. Could be an awkward conversation (because yous till admit you couldn't give it out from the suit) or not a conversation at all, because most furs do not talk within their suit (which I can very well understand) because it would break the suspense.
That's why I think their no real total solution. The safest thing I could think of is letting the whole species out of the equation till you had the chance to confirm in a later conversation.
You interact with the suiter. Later you can ask their spotter or someone that knows the suiter. Or the suiter themselves when they show up without the suit and with a bit of social engineering skills you talk about their character (you are already interested in their character so... why not ask more about them) and at one point you just ask "why did you choose this species and what kind of sub species is it?" Which would not give the person the idea you had no clue what species (or which of the choices you could think of) his or her character is.
However... I really really enjoy the spontaneous side of it. I enjoy the reactions you get when not talking to much and just use your voice to in a silly and entertaining way announce something you would like to do. Just shouting: "hiiii or hello" is just not the same.