The mark defines the intended filling limit for that reservoir. Filling above it can create spillage when the tank is fitted, the door moves or the water expands slightly with conditions.
What the observation tells you
An overfilled tank can make the lower door area wet without a failure in the refrigeration system. That does not mean every leak is harmless: damaged connections and cracks still need attention. Do not tip a full tank through an awkward removal path.
A useful next step
Follow the filling instructions using the correct water and quantity. Wipe accessible spills and note whether leakage persists at the proper level before requesting assessment.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.