I am shocked that your MIL's bank gave it back to her....they are not allowed to re-release couterfeit bills into circulation at all. I had a big fight with my bank about this. My DH did work for one of our neighbors (an elderly man) who went to his bank and withdrew $2100. I picked it up (still in the bank envelope w/his receipt in it) and took it to my bank to deposit it. They did the marker test on all the bills & told me one was a fake....I freaked out, it's impossible, it just came from another bank!!! They would not give it back to me, and would not help at all. They said it had to be sent in for testing to the federal reserve, and if it was legit they'd credit my acct. They never credited it to my acct either, and after many arguments with the bank manager their point of view is I could be making $100's in my basement, or know someone that is.....there is no proof otherwise. I couldn't even get it to take it back to the other mans bank cause they would not give it to me at all.