Nithya Bondalapati notes a discrepancy:
ARM (Azure Resource Manager) API does not support specific T-SQL resource naming formats and that’s why when Databases are created using T-SQL/SSMS, unsupported characters could get allowed into the names.
Azure Portal UI does not have this issue, because when you use Portal UI for creating a Database, the creation goes through ARM, and hence when unsupported characters are entered in the Name field, it immediately throws error, as shown in the below image.
None of the restrictions or onerous, but Nithya explains what actions fail or don’t quite work right if you have a database with special characters or ending in a period or space.