echo "You enter "$HOSTNAME". You can smell the wumpus." >> /etc/issue
echo "You enter $HOSTNAME. You can smell the wumpus." >> /etc/issue
Always quoting variables and command expansions is good practice, but blindly putting quotes left and right of them is not.
In this case, ShellCheck has noticed that the quotes around the expansion are unquoting it, because the left quote is terminating an existing double quoted string, while the right quote starts a new one:
echo "You enter "$HOSTNAME". You can smell the wumpus." |----------| |---------------------------| Quoted No quotes Quoted
If the quotes were supposed to be literal, they should be escaped. If the quotes were supposed to quote an expansion (as in the example), they should be removed because this is already a double quoted string.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.