Yes, Zenith indeed. They are not knob inserts, but rather the emblem that typically was next to the "Zenith" name on a color set that was equipped with a chromacolor CRT, so about 1970-79 chromacolor and chromacolor II sets. These would have also been used on the space command 600Z remote control (1974-79). A photo attached of a typical application of this emblem as seen on a 1972 portable Zenith color set.
1972 Zenith C3722W by
drh4683, on Flickr
1972 Zenith C3722W by
drh4683, on Flickr
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