[tapoxi]

There's a contact in Signal called "Note to Self" that you can use for this.

[WolfeReader]

I use Signal this way too. It's great for small messages and files. For larger files, you'd want SyncThing.

[hnarn]

Just hair splitting obviously but I don’t think it’s really a contact, it’s just what the recipient shows as when you send something to your own number.