[Mr70]

Here's a little info to help identify Chicago assembled Schwinn bikes for 1965 and newer.
The first letter is the month,and the second is the year:

Here's what the first letter stands for:
A=JAN B=FEB C=MAR D=APR E=MAY F=JUN G=JUL H=AUG J=SEP K=OCT L=NOV M=DEC

Here's what the second letter stands for:
A=65 B=66 C=67 D=68 E=69 F=70 G=71 H=72 J=73 K=74 L=75 M=76 N=77

..like Delco-Remy,it looks like they didn't use the letter I either.