Legal Question in Business Law in California

You can, at great risk. There is a huge body of law, and a great deal of litigation surrounding what is a permissible use of client or customer information obtained while at one employer when moving to a competitor. Taking them is not illegal. What you DO with them may or may not be, and is WAY beyond the scope of an internet Q&A.

Absent a confidentiality agreement literally prohibiting this, the California trade secrecy law provides a definition of "trade secrets" as information, including a formula, pattern, compilation, program, device, method, technique, or process, that (1) derives independent economic value, actual or potential, from not being generally known to the public or to other persons who can obtain economic value from its disclosure or use; and (2) Is the subject of efforts that are reasonable under the circumstances to maintain its secrecy. I doubt that a collection of business cards you personally received would be included in this definition. This is public information and is not (I presume) subject to compilation by your employer or maintained in secrecy by your employer.

Mr. Beal clearly has not done any customer list litigation. Who is and is not a customer or prospective customer of a particular company is absolutely a trade secret, whether that information is reflected in a collection of business cards or otherwise. I can all but guarantee you that if you use those business cards to start contacting your former employer's client or prospective clients from your new employer, and the former employer finds out, you will be sued and almost certainly successfully. One can only hope Mr. Beal's E&O coverage is paid up.

I agree with Mr. McCormick and suggest you be very careful. The employer may be able to claim that the cards you collected were in the scope of your employment, and done on the employer's behalf, not your own private interest.