The sign-in page is your shopfront
Clients see the sign-in page more than any other screen. It should carry your logo at a sensible size, your firm name spelled exactly as on your trade licence and a clear line about who to contact for help. A generic vendor screen here tells the client the software is not really yours.
Keep it calm. A white or light background with one accent colour reads as professional. Avoid stock photos of skylines; every firm in Dubai uses the same three.