I have three antennas on my roof: one is a CB antenna, and the two others are rubber ducky antennas for the radios. But my second rubber duckie isn't in front, it's on the passenger side, back a few feet behind the front door. That one is for the radio that is the outside entertainment center box.
If both rubber duckies are up front, and you don't have an obvious CB antenna, I suppose it's possible that one of them is for the CB? The only rubber ducky CB antennas I've seen have been on hand-held walkie-talkies.
Adam and Sue, and a pack of little furballs
2007 Holiday Rambler Endeavor 40PDQ Limited Edition - Cummins ISL 400
2013 Ford F-150 FX4 toad - USGear Unified Tow Brake, Roadmaster Blackhawk II Tow bar, Blue Ox baseplate
Home base near Buffalo NY, often on the road to a dog show