Crystals on bottle of sweet alcohol We've been given an old bottle of alcohol, an amaretto. 

At the top of the bottle, where the lid and bottle rim meet, a few crystals have formed. I'm guessing it's the sugars but am not sure.

Some one has mentioned they think the crystals forming means you should throw the bottle (and contents) away as it's not safe, but I can find no proof of this online.

Does the forming of the crystals indicate the drink is no longer safe?
You are right that the crystals are from sugar in the drink crystallising.

However, this happens very easily with liqueurs, or anything with a high sugar content, through normal use (liquid gets onto the rim, it starts to dry out and the dissolved sugar starts to crystallise on the surface).

It is not a sign that the drink is no longer safe. You can simply wipe the crystals off.