Mnh Zeppelin Set Signed On Back - What Is The Affect On Value For USA Collectors?

Craigk, these ugly expertising marks don't guarantee anything, if stamps can be forged, how difficult would it be to forge expertising marks? In fact, having expertising marks on stamps opens up another avenue for forgers to work on.

Aren't the c3a marked? Hardly a concern.

No more difficult than forging Stanley Ashbrook's signature.

"Aren't the c3a marked? Hardly a concern"
Assuming they are, if they only come that way, then you have no choice

Personally, I would buy these for the right price. I could care less what's on the back, the only thing I see in my collection is he front.

While I agree with everyone here saying they wouldn't buy them with the marks at the back, I equally feel that there are buyers who are happy to buy them at the full (or near) CV, who won't be bothered by such marks (might even find them an advantage). While I don't like the practice, if the stamp was right, the price was right, I would not reject it on that point alone. I have an easier time with that for used stamps than those with OG, but it's case by case.

I also wouldn't call the C15 - C17 "common", I would rather refer to them as "available". When OG stamps start to hit the $1,000+ range, they are no longer common... I wouldn't call a stamp with a value over $50 common... Common stamps are in the $0 - $50 range in my view.