What is a security?
If you are a traditionalist like me, you tend to reel off important legislation that was passed after the Great Crash of 1929. The '33 Act covers who, what and how securities get issued. The '34 Act concerns itself with how these new fangled securities can be traded. And the '40 Act covers the ins and outs of how investment companies work. If you want to dazzle the audience a bit, you might throw in the Howey Test that resulted from an SEC case in 1946. Or, for those in world of corporate finance, the curious case of the Green Shoe Manufacturing Company listing in 1919 cannot be overlooked.
But, those pieces of legislation (and other important bits that refined aspects), came after the concept of securities was well established. The idea of distributing tokens of ownership (whether equity or debt) to investors which entitled them to interest, dividends and/or voting rights, was well established. The New York Stock Exchange dates its establishment to the Buttonwood Agreement which was signed in May of 1792.