One of the rarest coins in the US-Philippine series is the 1906-S 1 peso. The mintage of this coin was said to be a good 201,000(ref) but before they were released in the Philippines, the value of silver has risen so sharply that most of the coins were shipped back to America to be melted. Many of the remaining coins were also damaged from being thrown into the sea when the Japanese invaded the Philippines. Luckily, an estimated 250 of them still exist.
I spotted this 1906-S peso being sold in eBay this morning for $1325. The seller claims the catalog value for this coin in EF grade is $3200. This coin is seldom auctioned off in eBay so you might want to buy it now!
Due to its rarity, many counterfeits of the 1906-S peso coin exist, some made from authentic 1903-S to 1905-S coins.
The seller gives us some tips on how to tell a genuine 1906-S peso.
1) All genuine 1906-S have the straight serif "1" . But beware of a shaven curved serif 1.
2) Check the number "9". The genuine pieces have a larger and rounder knob.
3) The number "0" which the upper inner loop to the right of the 0 is straight rather than oval.
4) Check the number "6" which the knob should be slightly in a teardrop shape rather than round.