What is "bicycle mail"

n. mail delivered by bicycle and identified by stamp and/or postal mark.

Bicycle Mail - The topic of Bicycle Mail can cover two separate and distinctive areas. It can be used to describe the Thematic ( Topical) collecting and or study of stamps bearing the image of bicycles, or more commonly used to describe a specific category of Special Delivery, where mail was delivered by bicycle and is identified by stamp and or postal mark used.