I've just stumbled upon the reverse image of an 1894-O Barber quarter. The mintmark seems a bit off, to say the least. It's extremely far to the right of the eagle's tail. I checked my 1892-O and the MM was right below the eagle's tail. Why did the Mint make this decision? Notice where the MM is. Weird, right?
There's so little clearance between the center of the tail and the R that it's hard to squeeze a non-microscopic mint mark in. Many of the Barber quarter issues have off-center mint marks. Lots of info about mint mark placement (and everything else) here: Complete Guide to Barber Quarters: Chapter 4: Date Analysis The 1894-O apparently has four known mint mark positions.
In addition, most MM positions do not add value, except for the 1897 S quarter, where the centered MM is more valuable
