Are savings bonds still earning interest considered "unmatured marketable securities"?

I do not think so; savings bonds, series A, B, EE, etc. bonds and private shares are non-marketable securities. The U.S. government offers both marketable and non-marketable securities to the public. Marketable securities, such as treasury bills and bonds can be purchased and resold to the public. But non-marketable securities, such as savings bonds, must be held by the holder until maturity and can't be resold to another party; they are Non-Marketable Securities as finding a party with which to transact business is often difficult; in some cases, these securities can't be resold due to regulations surrounding the security.

I didn't know savings bonds were non-marketable. Thank you for your prompt and thorough reply.