It is customary to write the letter het of a Sefer Torah, tefillin and mezuzah in the following manner: The sofer writes two letter “zayin”s, which are connected by a hatoteret, a “roof.” The roof is similar to a tree, which connects the two zayins. Although some sofrim make a straight line, the custom of most sofrim is to make a line that goes up and down, like the hump of a camel.
It is also- customary that the right side of the hatoteret is thicker than the left side. Also, a “tag” (crown) is drawn on the upper-left side of the letter, since it is customary to draw single tagim on the letters bet, dalet, hey, het, yud, and koof, often known by the acronym “bedek hayah.”
It should also be noted that when writing the two zayins, most sofrim round the top part of the right zayin. While some have the custom, when writing tefillin, of constructing a het from a vav and a zayin, this does not appear to be the common custom.
Summary: When looking at a het on the klaf of a Sefer Torah, tefillin or mezuzah, one should note the structure of the het, i.e., that it is made from two zayins, connected by a hatoteret, with a tag on the upper left corner.