a 'who called me?' variable?

[Dan Berdine <db002i@mail.rochester.edu>]

Is there an environment variable in bash that can be used to tell where 
bash is running from?  For example, is there a variable I can test in 
my .bashrc to tell whether I am running remotly, from a tty, from 
konsole, an xterm, etc.?  I'v looked at the Advanced Scripting HOWTO, 
but the only thing that looked promising was "$BASH_ENV" which seems to 
be empty.

Thanks,

-Dan