This is new since SAS 9.3 on how to display macro variable name and its value. Try to run
and you will get in Log window
You can read from SAS 9.3 online doc:
If you place an equal sign between the ampersand and the macro variable name of a direct macro variable reference, the macro variable’s name displays in the log along with the macro variable’s value.
In SAS 9.2 and prior, you should type the macro variable twice:
PS: it is called a “Tip” in SAS 9.3 online doc, but I’d rather call it a trick: not critical but nice to have (save your typing!). You may be also interested in Rick Wicklin’s differentiation on Tip and Technique.