The examples below are taken from two different texts. The first is from an MA thesis and the second is from an online magazine article.

You can see that the two texts both have signal phrases but the sources are cited in different ways. The MA thesis is an academic text and follows APA style rules. The second is a journalistic piece (albeit of an academic nature) and merely offers links to original sources.

If you are writing an academic paper, you should follow the academic style of citing your sources in whatever style (ASA, MLA, etc) your institution requires.