1. A computer-implemented method comprising: analyzing characteristics of a content item of a webpage to determine whether the content item represents a potential source of spam content, wherein the analyzing comprises: selecting, in accordance with predefined selection criteria, a plurality of hypertext markup language (HTML) tags of the webpage; creating an ordered sequence of the selected plurality of HTML tags; and applying a hash function to the ordered sequence of the selected plurality of HTML tags to map the selected plurality of HTML tags to a characterizing signature of the webpage; updating an occurrence count for the characterizing signature in response to the characterizing signature being generated; and when the occurrence count is greater than a threshold count, identifying the content item as spam content; and flagging the content item of the webpage as spam content.