BK-117 Airbus Helicopter pilot reported a Mast Moment Indicator exceedance during landing. Helicopter was taken out of service.

Narrative

While landing at the a hospital helipad; I felt the left front skid touch the ground which is normal for this helipad as it slopes up to the west. At the same time the skid touched the ground I felt the aircraft rocking aft and I applied forward cyclic to correct this; during that process I heard a Gong and immediately looked at the MM (Mast Moment) Indicator; which was coming back to the center; with the aircraft fully on the ground and stable. I didn't see any indication on the CAD (Caution and Advisory Display) of an exceedance (no MM Exceed light) and so I thought that I had caught it in time. I shut the aircraft down and we continued with the call. After I landed back at our home base (same as the destination for the patient); I thought again about the event and double checked the Mast Moment Exceedance page on the VEMD (Vehicle and Engine Multi-function Display) where I discovered that I did in fact have an exceedance. At that point I called the on-call AMT and took the aircraft out of service.Suggestions: I should have verified the mast moment page on the VEMD before loading the patient and transporting them back to our home base