B5 is 5% biodiesel, B20 is 20%. Your Sprinter will tolerate a tank or two occasionally.
If you have a choice between #1 and #2, always choose #2. #1 is gummy stuff your Sprinter can't handle. It's normally only sold in the winter as it contains chemicals to keep the diesel from turning into a gel in cold temps.
I would never assume that a pump that says #2, and isn't placarded, doesn't have biodiesel in it. I'd assume they're selling junky, gummy diesel. I usually avoid stations with pumps that just say #2. I had the check engine light come on after pumping at a station like that. The light didn't turn off until after I'd burned through a tank of brand name, 15 ppm, B0 (no biodiesel).