I rented an apartment and unfortunately without any notice rental management changed and I received a check with the new rental management company and me as a c/o for the amount of my security deposit. I was never notify that the old management company was going to mail a check for my security deposit and I didn’t receive any instructions as to what to do with the check, can I deposit it into my bank account? I have never heard of a c/o on a check.. please help!
c/o does not mean co-owner; it is a standard abbreviation for "care of" or "in care of". A typical address using this style has lines that look something like
New Slumlord Management Company, Inc.
c/o Renter's name
123 Any Street
Wherever AB 45678
meaning that the addressee (payee in the case of a check) whose name appears on the first line does not have the postal address shown below. The c/o, which appears on the second line lets the mailman (postman in nonUS parlance) know that the postal address is that of the person or entity listed on the c/o line, and that person/entity is responsible for forwarding the check to the payee. That is, the envelope/package has not been mis-addressed and should thus not be returned to the sender or disposed of in accordance with postal regulations for mis-addressed mail, but is to be delivered to the address shown.
This kind of stuff is fairly common practice. When I rolled over my 403(b) plan (Fidelity) to an IRA (Vanguard), I followed the standard protocol of asking Vanguard to collect the money from Fidelity instead of asking Fidelity to send the money to Vanguard. Vanguard made the request, but Fidelity sent the check payable to Vanguard Fiduciary Trust Company FBO Dilip Sarwate (Vanguard Fiduciary Trust Company is the official name of the IRA custodian of all Vanguard IRAs) c/o me at my home address rather than sending the check to Vanguard directly as Vanguard had requested. I then forwarded the check to Vanguard. Similarly, when I ask Vanguard to make a Qualified Charitable Distribution from my IRA (a facility available only to those over 70.5 years of age) to United Way of Champaign County, Vanguard sends the check, payable to United Way of Champaign County, c/o me at my home address for me to forward to United Way of Champaign County. I then send the check to United Way together with a properly filled out donation form so United Way can send me a receipt. (Note the absence of any FBO stuff on the first line). On the other hand, T. Rowe Price sends the check directly to United Way at the United Way address that I specify on the QCD Request form and tells United Way that the donation is from me so that United Way can send me a receipt. (Note to those unfamiliar with QCDs: there is no income tax withholding on the QCD -- the charity gets the entire amount -- but the QCD amount cannot be deducted on Schedule A as a charitable contribution. The amount does count towards the Required Minimum Distribution (RMD) but is not reported as part of the taxable distribution from the IRA on Form 1099-R and thus the QCD amount is not included in the Adjusted Gross Income: hence no Schedule A deduction of the QCD amount because it is not included in the AGI. But the taxpayer must keep the receipt from the charity along with other charitable contribution receipts in case of an IRS audit.)
So, the OP cannot cash the check or deposit into his account and then send his personal check to the new management company (unless he finds a very compliant or negligent teller); the check is not payable to him and the OP's bank should (modulo compliant or negligent tellers) refuse to accept the check for deposit or for encashment into currency (or void the transaction if the OP does new-fangled stuff like making a photocopy of the check with his banking app and using it to make the deposit electronically instead of in person at a bricks-and-mortar bank office). He should forward the check to the new management company telling them that it is the security deposit (and get a receipt from them) exactly as @prl says in a comment.