It is the same secret mark as is found on image Type A49a (see Scott #161).
The secret mark "is a small semi-circle in the scroll at the right end of the upper label" (quoted from Scott).
http://stampsmarter.com/1847usa/1870/BankNote10c.html
Don
re: #187 w/o secret mark & #188 w secret mark.
It is the same secret mark as is found on image Type A49a (see Scott #161).
The secret mark "is a small semi-circle in the scroll at the right end of the upper label" (quoted from Scott).
re: #187 w/o secret mark & #188 w secret mark.
http://stampsmarter.com/1847usa/1870/BankNote10c.html
Don