1870's Fifteen Cent ... Secret Mark?

Hello All

I have a couple of questions about the two 15 cent stamps below.
I have been to the StampSmarter web site ( which is a great site....thank-you )
but I still am not clear about the secret mark.
And I can not distinguish the difference between the hard grayish paper from soft porous paper.
Can someone please tell me which Scott number stamps these are.

Thanks
htx

This isn't really my best area of expertise, but I'll be the first to jump in. I think both these stamps are Scott #152 (hard paper, no "secret mark"). My knowledge may be outdated, but my recollection of the scholarship on this issue is that the so-called "V-shaped secret mark" is not a deliberate design alteration as in the lower denominations of this series, and so is an unreliable diagnostic. The example on the right also shows lines in the "hypotenuse" of the upper left triangle, an indicator of Type A51 according to the Weiss-Payton article at stampsmarter (BTW I think there's a typo in the stampsmarter article on this stamp--under the illustration I believe it should say "...as opposed to the A51a [vice A51] which is almost entirely white space.") If I am wrong about any of the above I apologize and invite someone with greater expertise to correct.

Hope this helps..

EXTRACT: The 15c WEBSTER ORANGE WEBSTER BANKNOTE IDENTIFICATION GUIDE PG 16-17
by Bob Pipes & Steve Einhorn ©2010 http://chicagostamps.com

Both look like soft paper Scott 189's to me.

Thank you all for your reply's.

I examined my stamps against the four diagrams provided and my stamps are either #163 or #189. Of course paper type was still a problem.
I tried the 'flick' method but I could not differentiate between the sounds. ( I guess too much loud heavy rock as a kid )
So I went to the bright light method and determined ( guessed ) that they were soft paper.
So I'll mount one in my book as #189.

Thanks again,
htx