As long as I can remembers, the rule has been that the title or caption, along with the footnotes, to a table or figure should provide enough information so that a reader can determine what the table or figure is showing without having to look for additional information in the text of the article.
This means that all symbols and abbreviations need to be defined either in the table itself or in the notes under the table, and the title needs to be very clear. And this needs to be repeated separately for each table and figure in a paper.
I have often asked colleagues at my university about this when serving on graduate student committees. The vast majority have responded that yes, this is a rule that they know about. However, it is apparently not one that they always think about when advising students (until I mention it) or when writing their own papers.
To me, this should be right up there with the formal referencing of sources that have influenced and informed an academic paper. Well, OK, may be right after referencing sources...
This post is #1 is a possible future series of Journal Editor Pet Peeves! -- Alan