It was common practice once upon a time to never put either an 'O' or an 'I' in serial numbers. Back in the 60s-80s, it was also a common practice to put a slas

It was common practice once upon a time to never put either an 'O' or an 'I' in serial numbers. Back in the 60s-80s, it was also a common practice to put a slash through a zero to signify that it was truly a zero.