First of all, congrats on your expo I guess, you're pretty excited. Those are big prints(?), if I may say.
I cannot say what would be the best way to sign your work but I can share how I do mine. I chop (stamp) my logo on the paper. It's a Chinese character engraved in one of those stones used by the Chinese. I place it on the bottom left hand side just after the print. My signature will be on the right side with number over the series - pencil. The signing and all are made before it gets mounted (I see that your works are framed already...) I also give a COA - it'll bear the other details.
In doing so, the signature and chop will remain on the work should the owner choose to replace the frame.
A friend of mine, signs at the back of the print itself and another signs ON the print - Vincent style, colored pen. Do not worry much if your sign won't be that evident. It would be better if your work would be admired THEN they'll find out it's you, rather than the other way around.
Whatever method you choose, be consistent. How you sign your works will also be your 'signature.'
Best of luck!