You are not obliged to remove your helmet unless it says on the notice next to the pump.
The above one means you wouldn't have to.
Have had this out with Tesco's (and I am not the only one around here), I never take mine off unless I've got to que for fuel.
Shell are not concerned if your wearing a lid.
Its like them refusing to allowing you to refuel while sitting on the bike. There is no inherent fire risk in doing this, but the regs that will be quoted are out of date, after the Fire research proved there was little risk