How to represent a collection of objects

I need to make some drawing to explain programming logic at the whiteboard.

I often need to manipulate collections of objects.

Which symbol can I use to visually show a collection ?

I wish to have an example for better understanding, because I was told to use aggregation/composition in UML style, but I don't rea开发者_开发百科lly see it. For instance, if I want to represent a collection of Object ABC...

Do you use an established symbology, or do you just ad hoc your drawings? Usually, I'd go for an entity-relationship diagram with a crow's-foot going from the collection entity to the contained objects, UML, or whatever the people I'm talking to understand. That last part is usually the key...!