Help with running RT-11 SAV files under RSTS/E

I have been interested, of late, in fixing some of the bugs in MACRO.SAV / CREF.SAV which the documentation shows also run under RSTS/E. In addition to fixing the bug so that the year outputs as 4 digits on the listing, I thought it would be interesting to run MACRO.SAV as a system job. This requires a mapped RT-11 monitor to use VBGEXE.SAV to load and initiate MACRO.SAV since it is obviously not an REL file. However, the goal is to still be compatible running under RSTS/E. My question is how to distinguish between a mapped RT-11 monitor and RSTS/E? Does anyone have sufficient information about the RSTS/E environment to be able to distinguish RT-11 from RSTS/E? TSX-PLUS is trivial since requesting the TSX-PLUS job number is not supported under RT-11, so that problem is solved. Jerome Fine