Spare A Dime. 20G. I will try and keep this somewhat spoiler free.
During The Reefer Madness case you will be finding out of circulation Silver Dollar coins either by suspects handing them over or finding them on suspects these have stamps on then containing 3 letters each.
Later at Parnell's Soup Co. Factory after investigating the two bodies Ray Pinker calls you over to inspect the coins you have found. Look under the microscope and put them in the correct order to spell out your next destination. Arrange the coins as follows:
1. The last coin on the right (MAS coin) moves to the empty slot on the left
2. The third coin from the left (ALS coin) moves to the last spot on the right
3. The first coin on the left (ANG coin) moves to the empty slot in the middle
4. This should spell (MAS)(ANG)(KAY)(MET)(ALS)
Your achievement should unlock here.