Were these used in the same manner as many signet rings, to create a signed impression in wax, and is faience suitably durable for that purpose?
Maybe and yes! The original purpose of scarabs was to mark (usually in clay) goods and documents. But they did adopt a decorative quality as well. In short, the signet ring form, in ancient Egypt, was derived from what you would think of as a signet ring, but I don't know if this would actually have been used.
More on the material: faience was certainly strong enough to make an impression in wet clay. This particular ring is actually made of steatite (a type of soft, grey stone) that has been glazed. It's commonly confused with faience.
Why does this have Ramesses's name on it?
Non-royal people, especially government officials, wanted to be associated with the king. The king was an embodiment of Horus on earth, after all. Demonstrating a close tie to the king would be an indicator of social status and have positive religious implications.