"ads". No apostrophe.
Remember the simple rule: the apostrophe indicates single ownership (the girl's cat) group ownership (the girls' cats) and word replacement (the girl is tall, the girl's tall).
The exception of course is "it's". It has an apostrophe with replacement (it is a cat, it's a cat) but not ownership (when referring to the cat's drink, you will only ever say "its drink", never "it's drink").
You may think this error is minor and inconsequential, but if you apply gentle and steady improvement to your grammar, reading your posts will be less painful. Please not that anybody who disagrees with me is poorly educated and wrong.
