Cees,
As has been suggested before, the SH most likely (and simply..) refers to a H2S or H2X-equipped aircraft. "Special" or "Stinky" H2S?
At that time the USAAF had no special prefix for Radar planes, the R then allocated to "Restricted" use a/c.
There were also B-24s with suffix "SH" after their type (B-24HSH/JSH), all with H2X. See e.g.
http://www.458bg.com/ac-agfishshoppe under Disposition.
Other examples are B-24HSH 42-51149 and B-24JSH 42-51955, both 453rd BG.
Please also see
http://www.b24bestweb.com/tigersrevenge2.htm, with many more on this website (enter H2X in search).
Groet,
Leendert