No, it's not my imagination! When I compare my two 3MX machines, I can clearly see that there's a difference in the way the logo's are printed on the mx's cases. And I have the pictures to prove it :-)
On the second picture you will see that this 3MX has the logo and the word SERIES more or less stuck to it. The letters and logo don't seem to pop out of the case. Psion clearly used a sticker.
Close up of the first 3MX:
Close up of the second 3MX:
And now the big question would be: did they start using stickers one day because they were a lot cheaper (I read Psion sold 1.5 million PDA's, so go figure) or did they use the stickers first?