That's right... the "blind bags" for the Tiny Turbo Changers actually do have codes on the bags.
Sure, there is a little window on the back, but with some toys having the same colours, and the enclosed instructions always getting in the way, an embossed letter has been found on the bags next to the tiny window, and that letter lets you know a lot more easily (and quickly) what toy is inside the bag.

From Allspark...

I found individual letter codes on each package near the small window (which also gives you a hint). The codes are:
A – Grimlock gold
B – Grimlock black
C – Lockdown
D – Hound
E – Bee yellow
F – Crosshairs
G – Blackout
H – Soundwave
J – Starscream
K – Sideswipe
L – Bee black
! – Prime
Yes, Prime seems to be an exclamation point.
It should be noted that Prime is most likely the letter "I", but the pressing of the letter onto the plastic may have made it look like "!" instead.
Either way, you can pick out Optimus from it being some sort of straight line.