Indeed, Critchley ZS symbols (Critchley Z-Type Cable Markers) are clip-on cable markers for identifying cables, conductors and equipment.

Specifically, the symbols +, – and / are available across four marker sizes (9, 11, 13 and 15), matched to cable diameters from 2.4–6.3mm. Also, each size and symbol combination is sold separately.

P/N: ZSPLUS