Civil War Patriotic Crest: Does Anyone Recognize?

A question for the Civil War specialists: What does the corner card on this civil war patriotic represent? Is it a unit insignia (North or South)? Or, is it something else?

Thanks for your help!

Hal

What is the date of the cover?
Consider
Cross Pattee
Union army 1st Division V Corps Army of the Potomac disbanded 1865

Fifth Army, 1st division used a Maltese Cross as its insignia in the Civil War.

Edited to add: Rod beat me to the answer!

rod222 - the cancel is unreadable. Thanks for your answer and help.

chipg - Thank you for your help.

Regards,
Hal

Hal, Looks like there is enough of a cancel there to figure it out. Can you post a close-up scan of the CDS for us? That, and crossing it against where those units were, should be fairly easy. At first glance it looks like Washington D.C. -Thanks.

This design is shown in Bill Weiss's book "Catalog of Union Civil War Patriotic Covers" on page 273 and is listed as CO-78, under the category of "Army Corps"

John Becker - THANKS for your response -- Sorry, the cover now belongs to a friend and it is not in my possession. I live in PA, he lives in FL. The cover was mine and sent it to him as a swap; otherwise, I would definitely accommodate. I will call him and see if he can do a close-up scan -- he's in his 80's and is "computer-challenged." Thanks for the "Washington, D.C." c.d.s.info -- he wasn't able to read the cancel.

KRelyea - THANK YOU for the info from Bill Weiss' "Catalog of Union Civil War Patriotic Covers". I understand it is an excellent resource.

wow that's dangerously close to the KKK's nonsense. I know it's an Army Corps insignia though. Cool cover.