Why do some series carry a dot [.] at the end of their titles? Is there a meaning to it or is it convention?
The punctuation symbol 。 is called a 句点 (kuten). Although it often functions like the English period (a.k.a. full stop), it is not identical, and is used as the punctuation mark for a question sentence far more often than the ? symbol is (the question mark is called 疑問符 [gimonfu] or はてな [hatena]. Historically, Japanese did not have the question mark, so although it exists in Japan now, it is not used in Japanese academic writing). In horizontal writing, the kuten is placed in the same position as a period would be in English: at the bottom right of the preceding character. In vertical writing, it is placed immediately below and to the right of the preceding character.
Wikipedia explains that
Starting in the 1980s, advertising copy writers began incorporating full stops in titles and other advertising. In the 1990s, the group Morning Musume (モーニング娘。) began using a full stop in its name, starting a fad for this usage.
Other cases include
As you can see, "Bakuman" is not a full sentence by itself, and "Nobuta. Wo Produce" intentionally slices a single phrase into two fragments by the placement of the kuten (Nobuta is the nickname of a main character that the protagonist decides to "produce," meaning to make-over Pygmalion-style. Grammatically, you cannot make "Wo Produce" into its own sentence), so these are both examples of a kuten that should not be interpreted as a period for ending a sentence. The kuten can be utilized as a sentence ender, but it is often used for style without any grammatical meaning. Similarly, some series titles make use of other Japanese typographic symbols for style such as , ＊, ☆, ♪, and ♯ (for example, うたの☆プリンスさまっ♪ [Uta no Prince-sama] and おジャ魔女どれみ♯ [Oja Majo DoReMi Sharp] and the choice of a star to be read as the letter A in ST☆RISH, an idol group in the former).