Go into your signature editor and type
'
[ url=http://www.rollitup.org]Whatever you want it to say here.[/url ]

Make sure to take out the space between the first bracket "[" and url=, also take the space between /url and the other bracket "]"

Put your link where the green text is, put what you want that link to say where the blue text is.

This is how I do it.

Edit: Also to change the color of what you want it to say, you just highlight whatever you put and change the color in the color palette above, the button with a big A.

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