Almost all classical and most modern caviar tins have rubber bands which surround the seems of the metal tin packaging. The rubber bands, often red in color, have traditionally been used for caviar packaging to ensure a hermetic (air-tight) seal around the caviar. This would then ensure that the precious caviar contained within would not be exposed to the air which would drastically diminish its quality, taste and ultimately self-life.
Beluga was signified with a BLUE rubber band,
Ossetra was marked with a YELLOW rubber band, and
Sevruga was noted with a RED rubber band.
Today however, these colors are seldom used to signify the type of species - Proper textual labeling has replaced this rudimentary style of labeling as there are now well over 25 different types of "caviar" sold throughout the world.