i need to write a notice on the matter of a lost dog. for this, i guess i do not need to provide any school or organisation. so, what should i write instead?

Such questions need to be attempted on your own to test your creative writing skills. However, these points might help you elaborate:
 
- You could write the name of the Community Center where you put up the notice.
- The notice could be put up on the board of an animal shelter. For example: PAWS ANIMAL SHELTER.