Beacons are clues that trigger some assumptions about the code, which most of the time is right, thus you save some mental expense.

Beacons could be a common naming. For example if a variable is named "node", odds are they will be an element of a tree or some other connected collection type.

You can enrich you code by glittering beacons in comments if they are difficult to implant them in the statements.

Remember, Code run on people.