If your MacBook Pro is directly connected to the server with an Ethernet cable (no other machines on the network) then you could just leave tcpdump running, showing source MAC addresses that are not your own. Just copy/paste this into Terminal:
MYMACTOIGNORE=`ifconfig en0 | grep ether | awk '{print $2}'`
echo "My own MAC address, to ignore, appears to be '$MYMACTOIGNORE'"
sudo tcpdump -pnei en0 not ether src $MYMACTOIGNORE | awk '{print $2}'
On modern computers, anytime you plug in an Ethernet, it's going to send a fair number of frames out, mostly multicasts and broadcasts, to do things like get a DHCP lease, verify it can use the IP address it wants to use, find its router, announce services it's offering, and check for other devices offering services it's interested in.
Just leave this running in a Terminal window as you plug your MBP into each server, and you'll see its MAC address show up in your Terminal window. Hit Cmd-K between servers to clear your Terminal window if you want to make it even more clear which MAC address is from the current server.
