Is the promissory note on a house a negotiable instrument [Article 3] or a security [Article 8]?
A promissory note on a house is a negotiable instrument. If it relates to a home loan then the bank files a security deed on the property or, in other states, a mortgage/deed of trust. These are not filed as UCC statements.
And its not the same as a federal reserve note or cash. The promissory note is secured by the real property.