That grease is usually excess from the front joint of the front driveshaft. MB switched to a different driveshaft vendor for MY00
and these all blew off a little excess grease during the first 10k.
If you look closely at the bottom of the transmission bellhousing and the side of the frame rail, you will see the same grease
tossed everywhere. Some guys have been tricked by this stuff and have removed the trannys thinking they were leaking only to be sorely disapointed. I wouldn't worry.

The label is for the front diff and it lists the gear ratio, vendor,
and needed lubricant.

DR.D