Objects that make you remember
Solution 1:
Memento
noun
- an object or item that serves to remind one of a person, past event, etc.; keepsake; souvenir.
- anything serving as a reminder or warning.
Example:
They offered tea, a smoke, and an Egyptian flag as a memento.
(Dictionary.com)
Definition №1 is probably most relevant here, even using the word you mention.
Solution 2:
A little old-fashioned, but still perfectly good, and in my opinion, rather charming:
Keepsake
something that helps you remember a person, place, or occasion: Her aunt gave her a little wooden elephant as a keepsake.
(Cambridge Dictionary)
I think this fits very well with the question (something that you keep to remember a moment or a place).
Solution 3:
Memory Trigger
It is a rather self-explanatory answer and to those who doubt it, this phrase is used: Ngrams
Those who were given the cassis smell remembered more details about the film and found their memories more unpleasant and arousing than those who had the background music as a memory trigger, although the lights and the smell were equally effective.
(Telegraph)
This would be used in a more scientific context and suggests a more official usage rather than a memento — a more homely item that you would keep on your mantelpiece.
Solution 4:
aide-memoire.
1.An aid to the memory, especially a book or document.
Example sentences.
‘His hundreds of sketchbooks were invaluable aide-memoire, and he kept them well organized so he could quickly locate what he wanted.’
‘These photos later served as aides-memoires for the large decorative panels.’.
Origin.
Mid 19th century: from French aide-mémoire, from aider to help and mémoire memory. — O-D
Solution 5:
Not quite what you're looking for, I think, but if it's remembering a moment or place in the sense of memorising facts, you may consider
mnemonic
noun
- a system such as a pattern of letters, ideas, or associations which assists in remembering something.