Neverdem is right, of course; that's one way to do it.
Much easier, simply deposit the shares into a brokerage account. Might have to deal with a mid-level brokerage, but the discounters **may** do the work for you. Stay away from Merrill and Salomon/Citi and that bunch.
The point here is that, if the broker wants you to trade something (a notion of which you should not disabuse him/her), then he or she is going to have to find out just exactly what those shares are worth, now isn't he?
SAJ is right.....I was a stock broker for many years...just I don't know where you live...but go into any discount type broker..Charles Schwab, TD Waterhouse etc...try and stay away from the Merrill Lynch's etc....you can open an account and not pay any fees...you can put the certs in the account and can tell you if they are worth anything pretty much right away....Preferred Stock does not appreciate in value like common stock...though it should have been paying out dividends for years....to someone....you can then sell it....keep it...the preferred stock is most likely expired but if common stock...may have some value.....those guys won't steer you into doing anything stupid with it and will tell you exactly your options