I respectfully XXXXX XXXXX your employee's business law professor.
Here is a link to California's UCC-1 form, for reference: http://www.sos.ca.gov/business/ucc/ra_9_ucc-1.pdf
A UCC-1 lien is used in financing transactions, but it is also used to signify that another entity has a security interest in personal property (as opposed to real property) that is located at another company.
Wen a company leases another company equipment (and I believe your loan of expensive equipment would be construed as a lease, even if you aren't charging for it), a UCC-1 lien is also appropriate. Please see section #5 of the California form.
Among other things, that puts other companies (banks and lenders, for example) on notice that your company actually owns the piece of equipment that is located at the company that has the equipment. Otherwise, it would be possible for the company you loan the equipment to use the equipment for collateral -- because there would be no notice that the equipment belonged to someone else. There are other reasons - for example, tax audits - that a UCC-1 lien would be desirable.
There are other types of liens that can be filed, but those would be filed with a County recorder's office, not the Secretary of State. That isn't going to put most people who would check that your company has a security interest in the equipment you are loaning.