Strictly from observation...
All of the guns I have seen that are signed "T. Ketland" or simply "Ketland" that do not have the "& Co." suffix are signed in Roman letters. I have seen the cursive engraved signature on a convex lockplate but it also had the suffix.
That said, I do not think it has any significance in this until later. Again, strictly from observation, most of the better quality locks have the name engraved in a cursive script while the "trade quality" locks have the name stamped on them in Roman letters. However, there are high quality locks with the name engraved in Roman letters. My feeling is that TK Sr. was a talented gunsmith and that, with his partner William Walker, moved from being someone that actually had a hand in putting good quality guns together, into a "gunmaker" in the traditional British sense of the word — someone that oversaw the making of guns and sold them both on the domestic and the export market. I do not think he had a "factory" in the modern sense. He did have a warehouse which was likely the lower floor of what had been his Birmingham house although he actually had two locations in the Gun Quarter from 1778. It is telling that, while he kept at least one of these properties (it was leased), he moved out of the city as he became more prosperous and the house was occupied by his brother-in-law and junior partner in the business, John Adams.
So, to answer the question, the real difference is in whether the name is engraved or stamped, not the style of the lettering.
On a totally different topic... I may have figured out who was behind importing the Belgian-made "fake" Ketlands c.1816 and later.