connected to LAN

[Jim Sims]

  I have several users of an application that is used over their  
specific company LAN.


If they are using a laptop, Mac or PC, and then move to a different  
LAN can I detect
that they have done so?  If they have done so, I need to have them  
save their data
in a different fashion.

I suppose I am asking if there might be a specific identifying item  
for a LAN that I can
obtain in order to do the above. I don't want to simply check for  
connection to a LAN but
connection to a specific LAN.

Network Novice here - please pardon if a naive or dumb question.

ciao,
sims