I'm not a lawyer but I play one on TV. Lol.
I had this exact same conversation with an attorney friend of mine some years back and his answer was No.
You are providing a service. It's the artist's or producer's responsibility to clear licensing.
Your job as an engineer is to hit the R button and to then mix the performances into a cohesive product. You are not responsible for the content. There is a slight possibity that you could be called in to testify as a witness if it went as far as litigation, but there wouldn't be any charges directed towards you. Unless of course, you were your own client. ;)

Thanks for the prompt reply.

So when they sign up with you to record, do you make them confirm they've got copyright on their stuff, or is it none of your concern?

I'm sort of in the same boat. A bagpiper I recorded a while back has some old reels he wants me to digitize. After looking into what was on the reels, it turns out they're of two pipers that are pretty big names in the bagpipe world, recorded when he was at the College of Piping in the fifties. He just wants to use them for personal listening. I'm not sure if what's on them would be worth putting out for historical record, or what the legal implications of that might be.

There is a section in the UK Copyright, Designs and Patents Act that covers unwitting copyright contravention.

97. Provisions as to damages in infringement action.
(1) Where in an action for infringement of copyright it is shown that at the time of the infringement the defendant did not know, and had no reason to believe, that copyright subsisted in the work to which the action relates, the plaintiff is not entitled to damages against him, but without prejudice to any other remedy.

The examples I can find link this with the defendant convincing the court with evidence supporting their stance - so if a client tells you the work is copyright cleared, you can't be made to pay any damages.

I have some material I recorded featuring a now famous person's pretty dreadful performance - but I dare not make it available, as I'm certain it's a shortcut to court as she has a BIG name record company now.

Equally, I have edited material provided me by an artiste, given to her by the BBC. The DVD has no copyright warnings on it, nor does the contents - but when I queried it with the artiste, she confirmed in an email that she'd been given the media by the BBC to do exactly what I was going to do - turn it into a showreel. I made an extra copy of the email, stuck it into the filing cabinet and did the edit. ironically, my edit then appears on numerous websites and even her management companies site - which wasn't part of my understanding (or fee!) It was for her own web site - so is that another misuse of rights? Funny really!

I suppose you could have some type of waiver written up - something that the client signs, stating that they alone are responsible for creative works clearance/licensing, and that you are responsible solely for the recording process, and have no say one way or the other, nor any responsibility, as to what artistic works your clients decide to record.

A simple one page document that indemnifies you from any legal action would suffice, something that simply states:

I, (client name), agree that I am solely responsible for obtaining clearance/permission/licensing, and for paying any fees or royalties to the appropriate party of ownership for (name of song).
(You or your company name) is not responsible in any way for any legal action, suite for damages/infringement, etc. that could arise from the use of this song in any way, legal, or otherwise.
In signing this document, I am relieving Your Name of any responsibilities, other than as a technical consultant of said entitled works.

And then they sign it, which you would then keep on file.

Don't use the above example. I'm not an attorney. Either research the language yourself, or, get an attorney to write something up for you. You may even be able to find something like this on a legal documents download website, such as [[url=http://[/URL]="http://www.lawdepot…"]THIS[/]="http://www.lawdepot…"]THIS[/].

In fact, there's nothing stopping you from having all your clients sign this type of waiver - if written correctly, it would protect you in any event.... should a client bring in some obscure song that you wouldn't know as belonging to someone else - another songwriter or publisher, etc., or, if they collaborated on it with someone else - who is maybe unaware that it is being recorded.

I think what you are looking for is referred to as a "hold harmless" agreement:

http://www.ehow.com/facts_5132661_hold-harmless-agreement.html