Marking the coins is a waste of time and energy:-) The coins you bring to the bank are going to be sent back to a counting house, dumped into a huge bin, get recounted and placed into new wrappers. Marked coins turn up all the time and I don't pay attention to them. I always find 1974 D halves, for example that are marked as searched and yet I have found 1974 D DDO coins in the same roll as a marked coin:-)
While I'm at it, (I shouldn't tell you this :-) You should be looking for doubled dies on all 90% silver, 40% silver and 1971-1977 dated halves. I am not talking about machine doubled stuff. There are whopper Doubled dies, both obverse and reverse on the dates in the range mentioned.
Have Fun,
foundinrolls