and therefore do not want to see any ad offering a bicycle, your path is simply to NOT search or browse in the "for sale, bicycles" category since if the ads are properly posted, nearly every ad there will be for a bicycles.
Instead search/browse the categories that are likely to contain the types of items you ARE interested in.
CL even offers the ability to "search all categories excluding specific ones"
Again, if you want to learn how to use the various powerful searching and filtering tools craigslist offers, go to the HELP DESK FORUM, and provide a detailed description of what you want to search FOR and/or what you want to exclude.
Be sure to identify the specific city/site you're looking at, and specific examples of ads that do (or do not) match the criteria for what you want to include or not.
Maybe even show an example of an actual specific search that is including ads you don't want to see, and then clearly identify some samples of the ads you don't want to see.