There is a famous story about a squirrel helping Sri Rama in building the bridge (Rama setu) to go to Lanka.
A squirrel sees Vanara army accumulating boulders and rocks for the bridge. A squirrel decides to help Sri Rama and picks up sand and pebbles. Sri Rama notices it and appreciates the effort of the squirrel and warmly stroked the back of the squirrel with his fingers. Since then, it is believed that squirrels have three lines on their body.
The moral of the story is to recognise and appreciate the help even when it comes from a small person.
This story is not a part of Ramayana written by Valmiki and Ramcharit Manas written by Goswami Tulsidas. These aren't the only versions of Ramayana. There are many other versions by many poets.
What is the origin of this story involving Sri Rama and squirrel?
From which later versions of Ramayana did this story originate?
Related question: Why do only Indian squirrels have stripes on them?