I'm going to setup another website on my host as a add-on domain. my questions are
- Is that a problem for seo? (Does it reduce the rank)
- Can visitors of new site identify any relation with other website? (I don't give any link)
I'm going to setup another website on my host as a add-on domain. my questions are
You worry too much.
If you add another site to your server or register an additional domain, yes, people and indeed especially search engines can figure it out. This is an important set of trust factors for Google at least.
This should not be a problem. In fact, under normal conditions, this is a good thing.
If you are running a good and honest site already, then adding another domain and having it associated with your existing domain adds credibility to your new site and helps to build it's trust rank. However, if you are running a junk site or spam site or other abusive site, then it will suffer for it.
This is not something you can hide from search engines especially Google.
Registration data is a major clue. Google, for example, is a registrar and can see the registration information for any site even with a private registration. Sites can also be associated on a network using analysis. There are also linguistic methods of associating sites. Other methods such as templating analysis, image analysis, application profiles, and other things that would amaze you can link sites.
I am not sure why you are concerned.
Most people cannot quickly tell that two sites are related without some work. However, for technical people who are familiar with what to look for, at least a level of probability can be established. I had done some investigative work in a copyright case that ended up shutting down some sites and open the original company up to many law suits. Keep in mind that this was a scam operation that tried very hard to hide the associations of their sites because the company was already in trouble in the courts and wanted to continue to scam people by using new sites. Their existing site was already under the careful watch of criminal investigators. In the end the company closed and the remaining sites sold to new owners who were required to operate under the eyes of the court for a long period of time to ensure that the site was not sold to cohorts.
It is a good thing that this level of analysis can occur. It is good for all of us.