(n.) One who, or that which, reminds; that which serves to awaken remembrance.

admonition adversaria aide-memoire annotation cue docket entry flapper footnote gesture hint indication intimation item jogger jotting keepsake marginal note marginalia memento memo memoir memorandum memorial minutes mnemonic notation note notice prompt prompter prompting refresher register registry relic remembrance remembrancer scholia scholium sign souvenir suggestion tickler token trophy warming