Your servo will work fine with the spectrum receiver. The sticker refers to the old airtronics receivers. I think most all receiver/servos now use the standard plug order which is signal wire on the end, positive in the middle, and ground wire on the other end. The old airtronics have the signal on the end, the ground wire in the middle and the positive wire on the other end.

Great servo, I have two that are in-use.