Well I got mine this summer, I didn't get the full self driving package and my car certainly doesn't see speed limit signs its very obvious they come from map data. It actually makes using AP in town a bit useless because they changed a lot of at the limits but somehow the map data is not up to date.
AP1 vs AP2 vs AP2.5 in the Tesla refers to image processing hardware and software.
https://en.wikipedia.org/wiki/Tesla_Autopilot#Hardware_1
The AP1 includes forward looking radar by Bosch, ultrasonic detectors and a forward facing Mobileye EyeQ3 camera at the rear view mirror mount. That camera does many things including rain detection. It also detects speed limit signs.
https://www.mobileye.com/uk/fleets/technology/speed-limit-in...