I agree with you - there is no need for the boss to post a notice using that language. It's unprofessional to say the least.
At face value, no laws have been broken however. Merely being offended isn't sufficient. The language used doesn't malign members of a protected class (age, race, gender, etc.) and as swearing goes, is pretty commonplace usage.
There is a possibility that the employer is pushing the envelope if someone objected on the basis of their "sincerely held religious beliefs" but that's about it.