It is against the law, as I said where I live. Fire code specifically.
"2205.4 Sources of Ignition
Smoking and open flames shall be prohibited in areas where fuel is dispensed. The engines of vehicles being fueled shall be shut off during fueling. Electrical equipment shall be in accordance with NFPA 70."
The "prosecution" is a fine if you are caught.
Also the signage you refer to is also per code\laws, the stations are forced to put those up...
"2205.6 Warning Signs
Warning signs shall be conspicuously posted within sight of each dispenser in the fuel-dispensing area and shall state the following:
1: No smoking.
2: Shut off motor.
3: Discharge your static electricity before fueling by touching a metal surface away from the nozzle.
4: To prevent static charge, do not reenter your vehicle while gasoline is pumping.
5: If a fire starts, do not remove nozzle—back away immediately.
6: It is unlawful and dangerous to dispense gasoline into unapproved containers.
7: No filling of portable containers in or on a motor vehicle. Place container on ground before filling."