What are the three letters either samechs or pe's which are at the end of the parasha in the Chumash?
See the article on parashah in Wikipedia .
Some extracts from it:
A parashah formally means a section of a biblical book in the masoretic text of the Tanakh (Hebrew Bible). In the masoretic text, parashah sections are designated by various types of spacing between them, as found in Torah scrolls, scrolls of the books of Nevi'im or Ketuvim (especially megillot), masoretic codices from the Middle Ages and printed editions of the masoretic text.
You have used the word "parasha" which does not fit this definition. What I think you mean is "sedrah".
In most modern Torah scrolls and Jewish editions of the Bible, there are two types of parashot, an "open portion" (parashah petuhah) and a "closed portion" (parashah setumah). An "open portion" is roughly similar to a modern paragraph: The text of the previous portion ends before the end of the column (leaving a space at the end of the line), and the new "open" portion starts at the beginning of the next line (but with no indentation). A "closed portion", on the other hand, leaves a space in the middle of the line of text, where the previous portion ends before the space, and the next portion starts after it, towards the end of the line of text.
In some manuscripts and in many printed editions, an "open portion" (petuhah) is abbreviated with the Hebrew letter "פ" (peh), and a "closed portion" (setumah) with the Hebrew letter "ס" (samekh), often in place of the visual gap in the line.
The five books of the Torah have been broken down into their weekly Torah readings for convenience. The weekly Torah readings always begin at a parashah break, with the single exception of Vayechi (Genesis 47:28).
This parashah break is signified by three "פ"s at the end of the sedrah. Eg here.
The end of the sedrah ויגש which is the sedrah before ויחי looks like this.