Hi @LeonordLim,
Regarding sign-in link, you can change it from here: https://github.com/edx/edx-platform/blob/open-release/hawthorn.master/openedx/core/djangoapps/ace_common/template_context.py#L18
For logo:
- add your variable for logo in template_context.py and use it in the template
or - You can override the template in your theme directory if comprehensive theming is enabled and Hardcode logo link.