Other tells on most rubber Ali straps that I've seen are:
1) the words "OFFICINE" and "PANERAI" are not cut as deep as in the gen straps
2) rep straps are slightly shorter than the gen
3) some colors are a slightly different hue when compared to gen (black, white, and olive green seem to be ok)
4) the strap itself is not as pliable as the gen, it definitely feels different on the wrist
5) there is a line on the cylindrical part of the strap where one part of the rubber mold meets the other (you can't see it unless you remove the watch head).
But as the post above mine says, for US$10 to US$15 (w/o coupons and shipping) it's actually a bargain.
For the most part, you can only tell the rep strap isn't the real deal when it's right next to a gen of the same color. On the wrist, I don't think anyone will notice (stay away from RWI regulars and you should be fine
).