The amber ones where side reflectors on the Norton and Triumphs at the time my Norton had them on when I brought it new, I think I still have them up in the shed and will have a look at the bracket they are mounted on.
The red one was mounted on or under the number plate, worked good if your tail light was blown when out at night, have you ever followed a bike at night that the tail light was out of action very hard to see the rider so the reflectors was a safety device for that reason.
Ashley