Welcome kah454, I found a nice Nihil Obstat logo somewhere, but lost it in the proces of searching. If I can retrace it I'll edit this post.
There is another way in which the word 'imprimatur' is used. In
oil painting, from the days of the Flemish Primitives till the second half of the 19th century when the impressionists adopted a more direct "a la prima" technique ( e.i. started directly from the white gesso coated linnen), it means a varnish mixed with brownish or greenish-grey transparant layer applied to take off the blatant gesso-covered white of the panel or canvas.
( about Rembrandt)
"The primer for the panels is white, probably glue-chalk gesso, covered with a transparent brown imprimatur of Burnt Umber mixed with varnish, which creates the golden glow characteristic of his work. His canvases are primed with a warm grey made from 'loodwit'(lead white with chalk, ground in linseed oil) and Raw Umber, or sometimes with white lead alone, with a transparent brown imprimatur."
