Reminder

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

Thesaurus Entries

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