Definition of "memento"

In conclusion, I would remark that the great railway stations of London deserve to be visited every whit as much as St. Paul's Cathedral, the Abbey, or the Tower, and they are as worthy a memento of this century as those buildings are of the days that are gone.

1944 July and August, “London Railway Stations in 1893”, in Railway Magazine, page 201, taken from The English Illustrated Magazine of June 1893

Many hospitals have not taken simple steps to lessen the distress and confusion which dementia sufferers' often feel on being somewhere so unfamiliar – such as making signs large and easy to read, using colour schemes to help patients find their way around unfamiliar wards and not putting family mementoes such as photographs nearby.

2011 December 16, Denis Campbell, “Hospital staff 'lack skills to cope with dementia patients'”, in Guardian‎