Tolkien is rightly famous for the languages he invented for Middle-earth. Whether they be Elvish (Quenya, Sindarin), Dwarvish (Khuzdul), or darker (the foul Black Speech of Mordor), they are an integral part of his secondary creation.
Almost equally renowned are the writing systems he came up with to write them by. The flowing Tengwar are frequently referred to as 'writing in Elvish' even when used to write English, and the Dwarven runes pop up in both The Hobbit and The Lord of the Rings. Dig a little deeper, and you'll uncover the Sarathi of Rumil, the Certhas Daeron of Doriath...
... and Gnomic?
Well, no - you probably won't run into Gnomic, and for good reason. It has only been published once, in an out-of-print issue of Tolkien newsletter Parma Eldalamberon (which I've never seen). It was paired there with Valmaric, for which there is a font which gives the letter meanings in its documentation, and the Gondolinic Runes, which are laid out here from their other appearance in Mythlore. But for Gnomic? There is nothing on the internet, nothing at all.
It's not perfect. Not every letter is present, and the writer seems to have been confused over the precise values of some of them. But it's enough to create the following glossary:
As can be seen, Tolkien presented two forms of Gnomic: a simpler version which is interpreted as carved, and a more flowing version that appears to be handwritten. Missing letters have been elided, though it is certain that H, at least, must have appeared (it's in pretty much all his languages).
The one letter I'm not sure of my reconstruction for is long i. The poem doesn't include any accented 'i's, but seems to switch randomly between the two forms of the letter. I would interpret the two handwritten symbols as identical, with just a pen-flick between them - but the carved letters are vividly distinct. Given that long O and long U are attested, a long I used mistakenly is the most logical reading.