The Siemens SIRIUS 3RT1900-1SB30 is a pack of 50 identification labels, 11 x 22 mm, in pastel-turquoise with a center latching design. These are the stick-on labels for marking contactors and other SIRIUS components in the panel, so you can identify circuits without peeling back wire markers.
These are identification labels — not a functional component, but a consumable marking aid. The 11 x 22 mm size fits the standard SIRIUS contactor and relay front plates. The turquoise color is a Siemens standard for certain voltage or circuit identification schemes; if your panel uses color-coded labels, this matches the existing SIRIUS palette. Snap-on or adhesive mounting to the component faceplate. No wiring, no DIN-rail space consumed — just peel and stick.