When Can I Put “Patent Pending” on My Invention?
There is no one way to emblazon, emboss, or stencil a patent pending mark. Nor is there a requirement for font size, or font type set, etc. The rules are subjective, but as the patent owner, you want to make it as obvious and apparent as possible without detracting too much from the design or commerciability of the product.
If you don’t have a physical product yet, and your invention is hardware related…make one! Haha, I know, its not always that easy – but you simply cannot label “patent pending” if you don’t at least have a prototype to affix the label or imprint it.
That said, if you are still in the planning stages, or if your invention would require a huge financial/time investment to build, you can create informational documents (digital or print) which will describe your invention and/or show it in diagrams/pictures. These documents should have “Patent Pending” on them, as soon as you have actually filed either a provisional or nonprovisional patent application.
Source: Bold Patents