A preposition is a word or a group of words that are placed in a sentence expressing the relation to another word (noun, pronoun or object) but in SASL are usually included within the sign.

Some examples : "above", "after", "before", "below",  "in", "on", "under", "in front of", "behind", "next to", "between", "to", "with", "from", "after".

In SA Sign Language, signs for prepositions IN, ON, UNDER, TO, FOR  are seldomly used and are typically indicated by the placement and movement of the L-Classifiers (Locative Classifiers).

You can get more information on the type of classifiers here: