Yup, I have had people look right at my gaffs and never notice the fact that they were gaffs and were still asking me how I did it too ha ha ha ha!
Edit: I have plenty of blank bicycle cards. I might go ahead and do Twisted Sisters with blank cards just to see what kind of reaction I get and to see if I actually get busted. If I do decide to do this approach, hopefully I won't get busted.
Edit2: It's a tough decision, because in my opinion, pyschologically when people see blank bicycle cards, they are going to think "Whaa? I didn't know bicycle made blank cards like that! And if they make blank cards like that, then they could more than likely make trick cards!" I have had good reactions with Twisted Sisters just using regular numbered cards (example being two of diamonds) which were of the opposite color of the queens within that packet. The idea being to subtly communicate that some kind of magical transpition took place, just using regular non trick cards. The backs of the queens of course would be opposite color of the rest of the backs in the pack as well, but the numbered cards would also be opposite color of the queen within that pack.
Yet, if you use blank cards and nobody challenges the idea that you somehow used trick cards, then of course, it is a very strong effect, yet it can be risky too, whereas some spectators who know of the existance of trick cards when they see blank cards, might decide to challenge you or immediately pick up the queens to examine them. It's risky, yet if you are not challenged it is a much stronger effect. Pros and cons to both approaches in my opinion.
Personally, I think it's probably best to stick with my original approach, but I might try the blank cards a few times, just to see how well it goes and to see if I ever get busted. You never know until you at least push the envelope. Yet taking calculated risks in my opinion is best. Whenever you use gaff cards, you are taking a risk, so you want to use them in a way in which the risk is in your favor and not the spectators. You want to use gaffs in a way where they won't suspect gaffs are in play, even if the spectator is aware of trick gaff cards. Performing in a trick shop is one thing, but in the real world outside the trick shop it can be a bit different in my opinion.