EMV (chip) card transactions are way more complex that you might think. There are 12 steps and step 6 is CVM (cardholder verification method) there are 8 options including signature and PIN (among others). The card basically tells the terminal what verification method to use so if your card is programmed as chip and PIN it will ask for a PIN but if it is programmed as chip and signature it will ask for a signature. That is the source of the confusion...different cards will require different actions to complete a transaction. It is not the merchants choice but the card issuer.

I have one card that is both PIN and signature so it will be interesting to see how that goes...