You feel discriminated against, try being a motorcyclist, plenty signs about saying "no leathers", "no crash helmets to be worn", "no bikers" etc
Morrisons petrol stations are one of the worst they have a policy to make you remove your helmet, sometimes before fuelling (even when using pay at pump), sometimes just when paying at the counter (including using the night hatch)......
No headgear of ANY kind (not helmets, hats, caps, hoods, etc.) or sunglasses allowed in banks or casinos. I expect the petrol stations are banning them for the same reason (to allow security cameras to get a full face shot and for the clerk to verify you are the same person pictured on your ID)