It should have a sticker saying so, and the fittings where you put in the 134 should be 134 fittings, which are much larger than the r-12 fittings.
95 SL500 Smoke Silver, Parchment 64K
07 E350 4matic Station Wagon White 34K
02 E320 4Matic Silver/grey 80K
05 F150 Silver 44K