This Hemingray-42 has an interesting "H" in Hemingray.
ANSWER: The faint embossing is caused by too hot glass where you can barely read the lettering, the glass tries to fold back into itself. ., mold paste filling the mold cavities. As for value, it all depends on who would want it as these insulators are unique.
Could also be a chipped letter in the mold stamping.
Thanks to Richard Case for the information.