How to Draw an Architectural Data Model in UML – was published recently by David Hay. It lists a set of guidelines to follow when using UML notation for data modelling.
For those using ER/Barker notation, he also published a set of guidelines a number of years ago – see Data Model Quality: Where Good Data Begins.
Both are useful resources and worth taking look at. Especially if you are thinking about creating modelling standards within your organisation.