1926 Philadelphia Sesqui-Centennial pane of 4, no gum, see Cinderellas page 9

"Cinderella" is a philatelic (stamp collecting) term which means, something that looks like a stamp (usually a perforated adhesive) and is not a postage stamp (it never had any postal validity- it could not legally carry the mail). Cinderellas include revenue (tax) stamps, poster stamps issued for advertising people (political), places (tourism), events (such as World’s fairs), and ideas (propaganda- often political, war, etc.). Cinderellas also include fundraising seals, such as Red Cross seals and Christmas seals. Many high brow Cinderella collectors draw the line at Christmas Seals because many are common, but admire other early fundraising seals such as Sanitary Fair seals, issued during the Civil War for aid and comfort of Union soldiers. I guess you can't collect everything, but there are plenty of rare interesting early Christmas Seals too!