Special Security Registration Number
The Special Security Registration Number (SSRN) is a unique number assigned to every registered foreign national.
Anyone staying over 59 days needs to register with Photo and Fingerprints, and about 700 pesos, at almost any Immigration Office in the country.
This is normally done, for those on Visitor visas, when renewing your visitor visa. It is worth checking that it is done, when renewing at near the 59 day mark.
An SSRN number is required for the Issue of an ECC, when leaving the Philippines after a stay of 6 months.
You must also have a mailing address for the sending of the SSRN certificate.
That address part might prove difficult for a tourist staying at different hotels for a total of just over 2 months, as one example.