What is the significance of anime characters' catch phrases? Uzumaki Naruto (Naruto) has a catch phrase "dattebayo". Ika Musume (Squid Girl) has a catch phrase "de geso". Himura Kenshin (Rurouni Kenshin) has a catch phrase "gozaru". And a lot more examples here.

What is the significance of anime characters' catch phrases?
Usually they're puns or just included for character. I think the aim behind it is to make characters more memorable.
Some of these pay off quite nicely for the series - Squid Girl's de-geso~ is instantly recognizable for fans even outside the show. The usage of it online or in popular media makes for good promotion for the series.
'de-geso', is a pun on Geso(tentacles) and De-gesu:

In end of Edo era and beggining of Meiji era, “De-gesu” is used by males of the lower class as transformational word of “Desu”.
“Geso” means tentacles of squid. Its article is mainly based on viewpoint of cooking. If your intention is to refer to Scientific aspects of squid, you would have to choose “Shokusyu” means just tentacle(s).
De-geso is the word combined De-gesu with geso. In the beginning of movie, Ika-chan spoke formally (but rudely) as the invader. So it is natural that she says manlike and old-fashioned terms like De-gesu. Of course, present Japanese don’t use such a word.
Traditionally, characterizing by making original suffix like De-geso was common technique in Anime. This is regarded as too facile nowadays.

De-geso~
Datebayo
Catchphrases could be used in order to emphasize a particular aspect of the character - Naruto's &quot;Believe it!&quot; (the frequent English translation) builds on his lively boisterous character, or in Sayonara, Zetsubou-Sensei &quot;I'm in despair&quot;, puts focus on the lead's suicidal &amp; depressional tendancies.
I'm in Despair!