How to Differentiate Left and Right 1961 Surround Speakers?

You've received your new speakers and you want to set everything up. But you can't distinguish the left surround from the right surround speaker as they are identical speakers! Well, not exactly identical, on the back of the speakers the label will tell you which one is right and which left as seen in the following picture:

While the incidence of mixing right and left would be minor using only 1 pair of surrounds, you need to be able to distinguish left and right when setting up back and surround speakers as discussed in the Placement of the TriAxial surround back-speakers article to have the in and out of phase set up accurately.