Question regarding Sign up, sign in and log in

Hi, 

What is the difference between the following expressions ?... I understand the meaning of each one, but in context for a native speaker ?

<ul style="margin-right: 0px; margin-bottom: 1em; margin-left: 30px; padding: 0px; border: 0px; font-variant-numeric: inherit; font-stretch: inherit; font-size: 15px; line-height: inherit; font-family: Arial, "Helvetica Neue", Helvetica, sans-serif; vertical-align: baseline; list-style-position: initial; list-style-image: initial; color: rgb(36, 39, 41);"><li style="margin: 0px 0px 0.5em; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; font-size: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; word-wrap: break-word;">"Sign up"</li><li style="margin: 0px 0px 0.5em; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; font-size: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; word-wrap: break-word;">"Sign in"</li><li style="margin: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; font-size: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; word-wrap: break-word;">"Sign on"</li><li style="margin: 0px; padding: 0px; border: 0px; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; font-size: inherit; line-height: inherit; font-family: inherit; vertical-align: baseline; word-wrap: break-word;">"Log in"</li></ul>

Thanks a lot.