How will you identify aground vessel from astern?

Not necessarily one will be able to identify AGROUND vessel, alone, by looking from astern. It is because there is a high possibility of mistaking it with vessel NUC making way. So, we have to look at other signs too. Most accurate way of determining the vessel is whether the vessel is having ground speed or not. Aground vessel will be having ground speed "zero" compared to NUC making way having certain amount of speed.