Also, if it is the coin you posted a pic of here already, it looks like it does have FS on it, so I don't know why you are saying it does not.
Ok, referencing your photo, I blew it up and cropped it and got this: I marked where the FS should be and if I am correct, there probably is some sort of small portion showing of this FS, even if it does not actually really look like this. To me, along with the overall appearance of this coin in your pic, looks to me as if it is just a very poorly struck one, either because of worn dies (where the FS also got worn out, somehow the die was polished at that point and over time you just don't see it on this coin (that the polishing marks are there) or that the initials got gunked up and on this coin the portion where the initials were are mostly filled with machine gunk, therefore not really showing the initials well). If any of the initials can be seen to be there or have been there, it is not an error where there is no FS (Felix Schlag initials) on the coin. Even if the initials cannot be seen clearly. Lots of things happen at the mint as far as dies being overused, etc. Many times this will cause distortion in features, etc. Then again, sometimes the use makes some feature poorer because of machine gunk getting into them. Outside of the mint, many things happen to coins to cause excessive wear in only a spot or two. This also could have contributed, I cannot tell from your pic. That area has a lot of stuff going on with it and a not very clear definition area below the bust. I won't say you won't ever have a coin that is a true error, but so far that has not happened IMO.
in real hand with magnifying lens maybe something is noticeable as soon as I think that it is a wear and tear that does not stamp FS well. Thanks KASIA for collaboration
This is another 1999-P. This might have full steps- if none of the dents and dings are so big that they cut entirely through.
Ron...imho, yours is 5FS...the contact mark across 5th line on the left side breaks the line between steps 5 and 6...Spark