Dropbox vs .DS_Store: prevent syncing
According to Dropbox's help, the .DS_Store files are not synchronised.


  Ignored files
  
  Some small system files aren't synced over Dropbox. These include:
  
  
  desktop.ini
  thumbs.db
  .ds_store
  icon\r
  .dropbox
  .dropbox.attr
  


If you want to manually delete all .DS_Store files, OS X Daily shared a how-to guide: Delete All .DS_Store Files from Mac OS X.