If you need to output to the terminal for normal logins in your profile/login file, but not break scp use, you can use the "tty" command - with the "-s" option it just gives you an exit status that tells you if the terminal is valid (ie. if it exists). An example for one-off echo commands in sh/bash like shells:
tty -s && echo 'this text only output when a terminal exists, so scp still works'
Or for more extensive output over multiple commands/lines, of course use:
if tty -s
echo other output