The concept of "lemon law" doesn't have a direct equivalent in American Sign Language (ASL).
Oh sure, you can just sign LEMON and LAW and those who already know and understand what a "lemon law" is will know what you are signing about. However, it will be helpful to understand a bit more regarding how to handle this concept in regard to how it may come up in everyday life.
The phrase "lemon law" is likely to come up when you or one of your associates buys a car that turns out to be a "lemon." Note the "quote" marks around the word "lemon." In the "Hearing" world English users understand "lemon" in context to mean a car that you have purchased that has many problems and tends to break down way before what would be considered normal.
In ASL we would begin by using signs to describe our experience with the car and then at some point someone may use the QUOTE sign or verb form of the NAME sign and then sign LEMON. Doing so is a way of introducing the concept of a car as a lemon.
There are those ASL purists who will protest and state "No, no, no! You can't use the sign LEMON to mean a type of car! You should fingerspell the L-E-M-O-N since you are not talking about the fruit!"
My response is that just as the English word "lemon" has expanded its semantic range (its range of meanings) to include a "bad car" the ASL sign LEMON can likewise expand its semantic range. This is particularly true when dealing with a two-word term or phrase.
There are those who will tell you that you should spell L-E-M-O-N and sign LAW.
Actually, I find it much more comfortable to sign LEMON and spell L-A-W.
Stop protesting for a moment and try it. When you compound the two concepts "LEMON" and "LAW" you drop one of the movements of LEMON and then spell L-A-W. The "L"-handshape used in LEMON moves off of the chin toward the location used for fingrespelling and morphs into an "A" and then a "W" by the time the hand arrives at the fingerspelling location. The whole compound sign can be done in a smooth quick movement with basically two handshapes (the "L" and the "W"). The "A" handshape is "there" but it is very transitory and lexicalized (blended in so as to look like part of the overall sign and not an individual letter).
So, then if you want to do it the safe way and avoid criticism from any ASL teachers, go ahead and fingerspell L-E-M-O-N and sign LAW (especially on first usage in a conversation or presentation). If you want to do it the quick, cool way as would be done by the typical bilingual Adult Deaf person living in a diglossic society (a situation in which two dialects or usually closely related languages are used by a single language community -- Wikipedia) then you can do it my way: Compound the signing of LEMON with the spelling of L-A-W (by dropping the second movement of LEMON and lexicalizing the spelling of LAW).
The following signs may be helpful to you as you discuss the concept of "lemon law."
LEMON
LAW
Notes: