Ben Nicholson White Relief Scultpure 1936 - version 1

means that it is equal to by definition.

In my EM text book it uses a equal sign with a triangle on top to define the intrinsic impedence of a lossless medium.

Ben Nicholson O.M. 1894-1982

T04119 sculpture c.1936 
Painted wood 228 x 305 x 241 (9 x 12 x 9 1/2)
Inscribed on underside ‘Ben Nicholson 193[...]-3[...]' towards t.l., ‘[symbol comprising an equilateral triangle above an 'equals' sign] 3 Mall Studio Parkhill Road London NW3>' b.l., ‘To | Nicholson | Chy an Kerris | CARBIS BAY | CORNWALL' circumscribed by a pencil line vertically on right and ‘BOTTOM' diagonally towards top centre