About SEO, is it safe to use rel nofollow on my sites pointing to each other?

I have 6 websites, all from the same niche, I would like to add a top bar on the home page of all 6 sites, with everyone's domain names, so that each website points to one another on the top of these sites: Our site network: domain1 domain2 domain3 domain4 domain5 domain6; If I use rel "no follow" will it leave me safe? I remember that years ago I did something like this without using "no follow", I saw the websites being harmed! I was practically interpreted as blackhat by having "a menu" that points to other sites of mine! A relevance fell a lot! In the folle is enough? Is there anything else I can do to make sure you do not get me wrong with search enginer?

<div align='center'>
<?php echo ("our others websites:"); ?>
<a rel="nofollow" href='http://domain1.com' rel="nofollow" target='_blank'> domain1 </a> |
<a rel="nofollow" href='http://domain2.com' rel="nofollow" target='_blank'> domain2 </a> |
<a rel="nofollow" href='http://domain3.com' rel="nofollow" target='_blank'> domain3 </a> |
<a rel="nofollow" href='http://domain4.com' rel="nofollow" target='_blank'> domain4 </a> |
<a rel="nofollow" href='http://domain5.com' rel="nofollow" target='_blank'> domain5 </a> |
<a rel="nofollow" href='http://domain6.com' rel="nofollow" target='_blank'> domain6 </a> |
</div>
We know what the nofollow is for, but even though we use nofollow, would not it be bad seen by search enginers to have a bar on each of my 6 websites, pointing to all 6 others?
Thanks all