Legal Question in Business Law in California

At this point, you cannot retrieve (i.e. repossess) the sign, unless your agreement has a provision to that effect. You might check the fine printo on your quotes or P.O.'s to see if you have a "security interest" in the product that you install. If so, you should have a right to repossess the sign. (You might consider such a provision in the future, if you do not have it, yet.) You may also consider whether you are entitled to protection under the laws of mechanics liens.

So, unless you have contract provisions that allow you to take back the sign, you are stuck with a straightforward breach of contract action. With only $2,100 at stake, I suggest that you use your local Small Claims court. Once you get a judgment, if the defendant doesn't pay, you can enforce the judgment by going after the defendant's property - including the sign you installed.

A seller's remedies for non-payment do not include taking back a portion (or all) of goods that have been delivered and are in the buyer's possession. The seller's remedies are set forth in Commercial Code section 2709 and 2710 and are limited to suit for the unpaid price plus incidental damages.

A seller can also reserve a security interest in sold goods under Division 9 of the Commercial Code. This would give the seller some recourse to the goods as collateral.

Just taking the signs back does not make you whole and is not a true remedy, assuming their value to you is well less than the unpaid bill. My recommendation is to file a small-claims suit and withdraw it if you are paid in full with a good check before trial.