Remember those colourful little flags that we could use in outlook, well gmail have them too. You can add different coloured stars and exclamations, done ticks, etc; you just have to apply them.
Go to your email account, click on settings in the top right corner and select the ‘labs’ tab and enable the ‘Superstars’ feature. Once you enable it, dont forget to save it (at the very bottom of the list). Then go to the general tab and simply drop and drag the icons you want to use into the ‘in use’ row.
You can also set your signature to go directly under your response as well as add extra colours for your labels from here; they are all in the ‘labs’ section.
Gmail Flags