The Rosewater Memorial is found on the promenade in Rosewater Park, just after meeting Maria for the first time in Silent Hill 2.
It is a memorial for sixty-seven people who died of an unspecified illness in Silent Hill's past. This may be the same sickness from the earlier days of the town when the immigrants from Europe brought a pandemic to the Native Americans (which is why Brookhaven Hospital was constructed). Evidence to support this is the claim that the bodies were dumped in Toluca Lake, as dumping bodies in a lake is likely something that would be increasingly unacceptable in future time periods.
If the game's "In Water" ending is canon, the Rosewater Memorial may serve as foreshadowing of Mary Shepherd-Sunderland's and James Sunderland's fate (although Mary more than James considering she has a disease).
Transcript[]
"In memory of the sixty seven
who died of illness and now sleep
beneath the lake."