While rereading a few finished journals, I noticed that my serious entries are easy to recognize, but my dry jokes can look downright mean years later. Tone disappears on the page faster than I expected. Now I sometimes add a quick note that I was laughing when I wrote something, mostly for future me.
A note that you were laughing helps, but it only conveys your tone. If a line could read as a swipe, a few words explaining what the joke was about can preserve the context too.
A small recurring margin mark could flag dry jokes without adding a sentence each time. Pick one cue and use it consistently, so it registers on a quick reread.