It's still in the picture data embedded. If you open the file in a HEX editor you'll see several adobe comments, one of them is "Digital Camera Fine Pix X100 Ver1.30".
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It seems as if there is some anti reflection coating and that doesn't seem to be very hard
Canon saved some $$$ buy just putting a plastic lcd into the 6d, the 5d3 has a glass cover ... so the very first thing after buying is to stick a protective plastic cover on it or order a glass protector, ebay/China for €5...
... but don't dispair, if you put a non-reflective cover on it now the scratch won't be as visible as now.
It's in a good condition, but some 3 years old now. I have some 13k shutter cycles. I'm trying to sell it with my Sigma 18-125 F/3.8-5.6 lens, a battery grip (from Phottix) and a second (3rd. party) battery.I hope you are able to get one and sell the 550D.
Personally, I chose to keep my old 60d with 150k+ shutter cycles when I purchased the 6d because it's not entirely an upgrade - the 6d lacks the swivel screen which is great for tripod, and the crop factor is very handy for tele (narrower fov) and macro (less dof). Last not least, not changing lenses but having two bodies is useful sometimes and you always have a failsafe if your 6d should ever break.
If your 550d isn't in pristine condition anymore you might also think about keeping it because the resale value probably probably isn't too great nowadays, the 18mp sensor is aged and newer models have many more features.