Thanks everyone, I had suspected the bankruptcy had wiped out all the old shares. How would something like this normally be sold if it were still good and how much would the 5 shares be worth? I would assume more than just the cost of five shares bought today, since dividends and stock splits should have added up after 26 years.
Those five shares are worth $0 on the stock market. Dividends don't factor into the 26 year old value of the shares, the dividends would be cash deposited into your account. The stock splits would just give you more shares; the splits affect your cost basis.
Most brokers will buy a worthless stock from you for a small amount (< $1) just so you have a sale transaction. Of course, they will charge you a commission on the sale! :-D Then you will have the purchase/sale data so you can file taxes. However, you need to know the cost basis of the stock so you can declare a long-term loss (26 years.)
Here is split/spin off data
Motors Liquidation Company - Historical Stock Splits / Spin-offs. In the last ~26 years there was one split in March 1989; it may or may not affect you depending on purchase date. However, there are three spin offs which will affect your cost basis. For Dec 97 Raytheon spin off you didn't own enough GM to get a full share so you were paid cash value of your fractional share. For May 99 Delphi spinoff you should have gotten 3 shares of DPH and cash for remaining fractional share. The DPH stock is worthless now (bankruptcy). In May 2000 you should have gotten 5 shares of GMH (Hughes) stock and cash for remaining fractional share. I'm not sure of GMH's fate but the ticker is delisted. Hughes is still around. The value of these spin offs reduce your cost basis. Twenty six years ago (6/5/15) GM stock was $40.50 so the pre-spinoff cost basis was $202.50 plus commission (just an example, only applies if 6/15 was really your purchase date.)
Once you figure out your cost basis you can figure out how much you will save on your taxes vs selling the certificate as a collectible. Or maybe the sentimental value is higher.
For the stock to be good it would have to be stock in General Motors Company (the new GM). On Friday, 6/5/15 it closed at $35.12 so five shares would be worth $175.60. It would be sold just like any other stock on a stock exchange using a brokerage account.