These stickers – made from Scotchlite – work by reflecting light shone at them (car headlamps). Unlike some reflectives, however, they stick to a variety of surfaces and can be as temporary or permanent as required.
Respro advise that they be fitted to clothing, although I’d shy away from some technical garments just in case. They can also be applied to helmets without risk of structural damage and I found them particularly effective as a supplementary lighting system along unlit roads. Adhesion on cotton duck panniers seemed good and appeared to highlight my presence to other road users sooner.
They’re particularly good on gloves, especially if your winter pair is dark: a few well-placed strips will make your signals hard to ignore.
Good supplementary lighting systems are as important as main items and I was particularly grateful for them when my lead acid lighting system began to dim 20 minutes from home. Fit them to the winter bike, your helmet, your panniers and even gloves, but be very cautious about applying them to your best technical kit.