Signoffs
I do mean Nos. 21 and 22, under Flight Instructor endorsements, as follows:
                 Flight Instructor Endorsements
      21.  Endorsement for aeronautical knowledge:  FAR Section
      61.185(a) and (b)
      I certify Mr./Ms.___________ has satisfactorily completed the
      course of instruction required by FAR Section 61.185(a)(1)
      through (6), and has logged the ground instruction required by
      FAR Sections 61.105(a), 61.125(a), and 61.65(b) in preparation
      for the flight instructor (airplane/instrument) rating.
          S/S    [date]    J.J. Jones     654321CFI      EXP. 11-30-91
      22.  Endorsement for flight proficiency:  FAR Section 61.187(a)
      I certify that I have given Mr./Ms.___________ the flight,
      instruction required by FAR Section 61.187(a)(1) through (6) and
      find him/her competent to pass a practical test on those
      subjects.
          S/S    [date]    J.J. Jones     654321CFI      EXP. 11-30-91
I copied and pasted these directly from the FAA page I gave you above. 
The following URL will take you directly to Part 61 and you can look up the specific references:
http://www.access.gpo.gov/nara/cfr/waisidx_99/14cfr61_99.html
I thought about the 60-day bit some more.  I've seen that put on an endorsement.  On the other hand, by operation of regulation your signoff is certification that you gave your student instruction within that timeframe.
Just the same, you'll be fine if you stick to the AC signoffs.
Once again, hope this has been helpful.