DO NOT DO THIS -- IGNORE WHAT THIS ARTICLE SAYS
I manage most of the corrections and game submissions, and using this method to track what games should be merged is inefficient and ineffective. The easiest way to get a game considered for merger is to use the Submit Corrections button in the game entry. In the form, use the message to admin box to explain what game the game entry duplicates. The submission will be reviewed, and acted upon. - Skelebone
The below is kept only for historical purposes, do not use this method to mark up games for merger.
Occasionally, the same game, published under different titles, gets entered in the database twice. In that case, the games need to be merged by the admins. If you identify games that may need to be merged, edit their descriptions and add text to the effect of "This game is the same as this other game and is a candidate for merging." By checking the backlinks (via the "What Links Here" link in the lower right) we can see candidates.
See also "candidate for splitting".
What constitutes the "same game"
Of course, the database has some similar games with different entries which are chosen not to be merged. The general rule, though not a strict policy, is that if the gameplay is identical or nearly so, and the components are identical or nearly so, it is the "same game".
See the Same Game Policy.