SQL Server - Is it possible to forbid creation of default constraint name?
I think you could use a DDL trigger if you could build a reliable LIKE expression that determines that a column has been specified with a default but does not contain the word constraint before the word default. But that won't be very fun. If you don't have PBM you're probably better off just manually reviewing the DDL in the default trace or having a DDL trigger that e-mails you on create/alter table, and slapping wrists when it happens.

(I mean, how often are people creating tables in a way that violates your corporate naming standard, and why are they still allowed to create tables if they can't follow the rules?)