Slackware :: Detecting An SSH Session

When in an SSH session I modify my command prompt by appending (ssh) to the command prompt string. Works nicely to remind me I'm in an SSH session.I also modify the prompt command by inserting the host name, but the (ssh) string really helps.Works nicely until I run the su - {username} command. Using the "-" option ignores the original SSH environment variables that are created.Of course, when not using the "-" option then the original SSH environment variables are preserved.Any ideas how I can determine I am in an SSH session to modify the command prompt after using the "-" option?