Hii

please let me know ur requirement and wht format you are asking for ( Is it a offer letter or an agreement form)

not only birthday cards, you can also decorate their cabin with flowers and cards signed by all associates or from particular department staff.
If your company permits you can have a get to gather of all associates by end of the day and celebrate birthday party or else just appreciate them at all employees.
We can conduct more and more if funded by company, even you can go for free of cost appreciation to associates feel happy.