I’ve noticed that in this U.S. primary campaign, all television and radio advertising by the candidates contains a section where the candidate says “I’m blahblahblah and I’ve approved this message.”

Apparently this is required by law, as the result of the Bipartisan Campaign Reform Act of 2002 [PDF] that states, in s.311 (3) (d) (1) (a):

Any communication described in paragraph (1) or (2) of subsection (a) which is transmitted through radio shall include, in addition to the requirements of that paragraph, an audio statement by the candidate that identifies the candidate and states that the candidate has approved the communication.

And in s.311 (3) (d) (1) (b):

Any communication described in paragraph (1) or (2) of subsection (a) which is transmitted through television shall include, in addition to the requirements of that paragraph, a statement that identifies the candidate and states that the candidate has approved the communication.

Thanks to IsleAsk for research assistance.