God speed is a old phrase which means God prosper you or good fortune, said especially to those starting out on a journey. This is particularly apt for Greenock which was once a major port, with ships and mariners travelling to all corners of the globe.
Other elements of the coat of arms also relate to this great maritime past, the sailing ship being the most obvious one. Greenock was once a major centre for herring fishing - thus the three fish.
This depiction shows men with barrels - again, many herring were salted, encased in barrels and sent all over the world from here. Many other goods were imported by ship to Greenock, like tobacco and sugar, processed here and then exported worldwide on local ships.
The set of three covered cups or goblets is the emblem of the old local land owning family, the Schaws. They were reputed to have been Masters of the Wine Cellar and Cupbearers to the Kings of Scotland. This job meant that they had to taste the king's wine before he drank it to make sure it didn't contain poison! Haven't heard of any of them dying while employed in that capacity - a dangerous occupation in troubled times!
All these depictions of Greenock's motto and coat of arms come from inside the Municipal Buildings in Greenock which were completed in 1886.