TL;DR: If the daily reputation cap is reached, on the reputation tab you can see upvotes that no longer increase reputation (or contribute less than the usual +5/+10). It might be useful to include somewhere on the reputation tab the information why this is the case. (Only if the daily reputation limit is reached - we do not want to add there too much redundant information that the users actually do not need.)
Often when users reach daily reputation cap and no longer get reputation from upvotes, they are confused why this is the case. Anyone who is sufficiently active on some per-site-meta have seen questions asking about this. It might be helpful to users if this information is shown somewhere on the reputation tab - this is the natural place where to look when somebody has a suspicion that something is off about their reputation changes. (Of course, this information is completely unnecessary if the user did not reach the limit - so it should only be displayed for days when it was actually reached.)
I am not exactly sure what would be the best way to achieve this. But perhaps the tooltip on upvotes on reputation tab which currently shows "answer was upvoted 1 time" or "question was upvoted 1 time" could include information about the reputation cap for the upvotes which no longer add reputation. (The screenshot below show how it is displayed at the moment.) Maybe a tooltip over some other part of the reputation tab would be a reasonable solution? Or perhaps somebody can think of better way how to include this information so that it would be visible. (I am not saying that it necessarily has to be a tooltip, but that seems like a solution that is not "too shouty".)
I decided to ask this after a recent question on Meta MathOverflow - 5 points for an upvote to an answer? - and a subsequent discussion in chat. (The example in the screenshot is also taken from this instance.) But I am pretty sure that questions about this appear on many per-site-metas - I have seen similar questions on the few sites that I frequent.