In addition to @F. Hauri answer, I prepare useful "LoggedIn prompt".

One additional file is optional ($HOME/.ssh/users):

 kszumny@laptop kszumny
 kszumny@comp2 kszumny
 tom@laptop tom
 pati@home
 chris@workstation1 chris
 chris@workstation2 chris


This part should be pasted to `/etc/profile` (for all users) or to `~/.bashrc`

 other_users_prompt()
 {
 pids=`ps fx | grep "sshd:\s" | awk '{print $1}'`
 users=""
 for uid in $pids
 do
 ssh_crtFp=`sed -ne "/sshd.$uid.:.*matching .SA key/{s/^.* //g;p;q}" /var/log/sshdusers.log`
 for ((ssh_i=1;ssh_i<=$(wc -l <$HOME/.ssh/authorized_keys);ssh_i++));do
 export ssh_line="$(sed -ne ${ssh_i}p <$HOME/.ssh/authorized_keys)"
 echo "$ssh_line" >tempKey
 export ssh_lFp=($(ssh-keygen -l -f tempKey))
 if [ "${ssh_lFp[1]}" == "$ssh_crtFp" ] ;then
 export SSH_KEY_USER=${ssh_line##* }
 ST_USER=`cat $HOME/.ssh/users | grep "${SSH_KEY_USER}" | awk '{print $2}'`
 if [ -z "$ST_USER" ]; then
 ST_USER=$SSH_KEY_USER
 fi
 if [ -z "$users" ]; then
 users="$ST_USER"
 else
 users="$users\n$ST_USER"
 fi
 break
 fi
 done
 done
 
 if [ `echo -e "$users" | sort | uniq -c | wc -l` == 1 ]; then
 exit
 fi
 
 users=`echo -e "$users" | sort | uniq -c | awk '{print $2"("$1")"}' | xargs echo -e`
 echo -e "[LoggedIn:$users] "
 
 }
 
 PS1='$(other_users_prompt)\u@\h:\w\$ '

**Result**

![enter image description here][1]


 [1]: https://i.sstatic.net/I1Xua.png