Anyways to log a valid smiley at this challenge you need to fulfill two requirements. First you need to find the cache's container and sign the log. Second you need to fulfill the requirement listed below.
Find ten caches on their anniversary day, which is at least 1-year after day the caches were hidden. To verify your finds include the list of ten caches' GC codes and the day of your find so I can visit those caches' pages to check and match the hidden date.
Some rules apply to this challenge tho. Event caches do not count towards the challenge. So the following caches cannot be included in the list of ten caches to fulfill this challenge: Events, Mega events, CITOs, 10 Years! Events, and GPS Adventure Maze Exhibits do not count. The ten caches you wanna use to complete this cache must be at least 1-year old so FTFs on the same day the cache was hidden cannot count towards the challenge.
Although you can use any cache that you already found I am afraid that you cannot include a cache that you found twice. Only the first find on any cache will count towards this challenge. That is why the difficulty is high but the terrain is not that high.
The cache is retro active so you can use any cache you found before. I am sure you may use some app or tool that helps you sort through your list of finds. Some oldies you already found may help you and save you time if you decide to take on this challenge. Thinking about it the challenge is not easy and it may require careful planning.
Second FTF
For the hardcore geocacher I figured that this cache may give a second FTF, which will be harder to achieve and it may require patience. To obtain the second FTF on this challenge you will need to include in your list of ten caches one cache which birthday is on February, 29th. Remember that you will need to find this cache at least 4-years after it was hidden if not more. If you already fulfill the ten caches, you may add the February 29th find to the list and scored the second FTF. Please post the GC code of this special cache so I can visit the page and read the logs.