Half-Life Easter Egg - The Military Can't Spel Rite

In mid- to late-game, there are several spray-painted messages on the wall directed at Gordon Freeman. I know of three. All are in areas extremely dangerous to the player.

These are in the section 'On A Rail'. One of them is "Surrender Freeman" - partly hidden found on the wall by a machine-gun bunker. Another is "Die Freeman" - over three laser-trip mines over the track.

As appropriately placed as these are, they are not eggs. Here's how to find the one that is:
At some point, you will see a small bend in the track ahead. Just before that bend is a metal door and a small platform. WARNING- there is an automated tripod gun there. Attack with extreme caution.
After dispatching the gun, stand in front of the door. Open and start shooting as a bullchicken (the green, gunk-spitting aliens) is just beyond it.
Proceed to the end of corridor; there are ammo pickups but also several headcrabs and a barnacle to deal with.
Turn around and turn on your flashlight. In a small recess to your left is the message "YORE DEAD FREEMAN". Looks like someone forgot their spelling lessons in Basic Training.
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I know this isn't earth-shattering, but it qualifies as an Egg because:
1.It isn't normally visible to anyone who plays through the whole game (unlike the previous two)
2.Most players will give up trying to enter a very dangerous, dead-end corridor unless there is no other place to go. You have to knock off the tripod gun, the bullchicken AND 2-3 headcrabs before even looking around. More work than most would do in the game for a few ammo sticks and satisfying curiosity.