As a beginner, I practice two forms of meditation: one focusing on the breath (typically with eyes closed), and one focusing on a colored disc (kasina), obviously with eyes open (unless cultivating the after-image). All descriptions I have seen for the former describe the arising of the counterpart sign when the eyes are closed. However, from what I have read on kasina meditation, the counterpart sign seems to arise with the eyes open. I have not experienced either of these myself (and in fact, this link dismisses its importance altogether), so I would like to ask: is it possible for nimitta to form iin either case?
I do not practice Samatha also from what I have heard:
Generally you don't get the counterpart sign with eyes open, but there may be cases of practitioners who can enter the Jhanas with eyes open. Perhaps more among people who do the Akasa Kasina. (If I remember write in a chronicle late Ven. Ananda Mitri Thero mentions such a Yogi doing the Akasa Kasina) In actually what needs to be done in Kasina is to create the perception of the meditation object in your minds eye. If it is Yellow, create a yellow circle in your mind. To do this generally it helps to have your eyes closed so you do not have any distractions.
Another observation of the 2 links is: one in on Kasina and the other seams to be on Anapana. (I only skimmed through it.) So what is said for Anapana may not be generalised to Kasina.
Having said this, on a site note, it is advisable to always have a teacher when doing Samatha. It is generally dangerous to do by just reading books or material you collect from forums or the internet. If you are in US maybe you can try: http://www.imsb.org/. Perhaps the teacher can teach Kasina. If you are in some other location try: http://www.buddhanet.info/wbd/. The Pa Auk tradition generally train their followers in all the 40 meditation subjects (you have to choose a suitable subject for your self), hence try to see if you can locate a teacher in this tradition in your area.
The proof of the pudding is in the eating, no matter how many books are written about the pudding. Once eaten there can be no mistake about it.
As a samatha meditator, both the signs exist for both types of meditation and which still appear when the eyes are open if they are vivid.
Having said that I've quiet a few fellow meditators who do not see the signs but continue to develop Jhanas using feeling.
It might vary from meditator to meditator.
The following quote is from the book "Practicing The Jhanas" by Tina Rasmussen and Stephen Snyder. They were both students of Pa Auk Sayadaw and undertook a Samatha Meditation Course under his guidance. They write in the book that they achieved the 4 material jhanas and the 4 immaterial jhanas.
Here is a description of Tina Rasmussen's practice where it's talked about her being able to see the nimitta with open eyes:
"... The nimitta will arise more and more often as continuity of practice continues. It will gradually increase in size and be present more continuously throughout sitting meditation and even while the meditator is moving around with eyes open. We each had the experience of seeing the nimitta, on occasion, when our eyes were open while walking or eating. For Tina, at some points the nimitta was visible consistently while walking around with eyes open. This is not required or necessary but can happen. Once the nimitta is present for the duration of nearly every meditation period, it is considered to be stable... "
-- Practicing The Jhanas, Ch. 4, p. 181