The answer is, NO it's not forbidden, there's a cabalistic method,
I read in the book of rabbi Aryeh Kaplan, (Meditation and Cabbala)
Quotes Rabbi Yitzschak the Blind a great Spanish Cabbalist saying the following,
Picture the four letter name in your mind, both hays of the four letter should have a crown (like that of the tora) from there, your heart needs to meditate on the "Ayn Sof" = The infinite one. Your mind and heart MUST at all times be connected, meaning on the same page. Following warning, please be very careful, utmost caution must be taken care of on your location, it must always be clean, and your hands clean/pure.
If you are strong enough to hold it, you can be like such the rest of the day.
There's a rabbi on YouTube, whose name is Rabbi Ariel Bartzadok from kosher torah school, he has nine videos, on how to use the name for many more than just picturing it, you can fight evil, reorganize your thoughts and so much more.
Please go to the following link, the videos with the name in the background are videos.
Here's a secrete, If your strong and sensitive, you can experience what it feels like to be in the presence of g-d, as your continues meditation will bring the vibration up, hence being in the presence of such, this will also be the reason why you must be clean at all times. It's not a joke and should be taken seriously or you can very well be profaning his name.
So what does it mean to have pure hands?
Please note (If you do have to do the following, you have go and rewash with the netilat yadayim cup, the ritual form of washing).
No scratching the head or any part of the body that is usually covered,
No nose picking,
No touching of anything that is impure, like garbage, or anything that has a foul odor, cleaning (that requires you touch things that are not clean)
Touching your shoes, soul of the shoes or even feet.
If you passed gas you must remove yourself from the location to where you can't smell the foul odor.
Needles to say, dead bodies, people that did not wash their hands in the mooring, or after using the washroom.
(Shulchan Aruch, orach chayim, hilchot teffilin, tefilot).
There are those that are extreme or for a better way to put it, have a different philosophy, that is, g-d is with me, in heaven and in hell, when I'm clean and when I'm not, because there's not a place where he's not, not only that, our bodies naturally produce foul odors within, that we can't do anything about, so he's with me when I'm clean and when I'm not. NEVERTHELES you must not and can not just jump into this different method as you lack experience, and credibility in heaven to be granted such leniency. Again to be tricked by those that will come and argue by saying that the statement still stand, there's not a place where he's not... As that is true though, that does not mean we can do as we wish, as there are boundaries that we cannot surpass unless we have created that authentic connection with heaven and g-d. Besides these individuals, have a very strong connection with the presence and not the image that we just spoke about, they can transform the impure energy through learning and doing great positive deeds.
If you're going to be mediocre or unwilling to, then please hold this to your prayers and personal moments that you would like to connect with him.
What is mediocre, don't treat the image with a lazy attitude, with a lesser mind, i.e. depressive, or just simply not giving the proper grander to that is required to give to his name (his presence) This is almost forcing you to always be happy, and or be a great person, this is done by expanding yourself to a great degree, as in whom you are as a person that g-d created, and dedicate to him and so on.
Why is this important, because your are inherently going to activate a very powerful energy, that you CANNOT disrespect, and by Disrespecting yourself you are by default disrespecting his name causing a major sin, that may be considered irreparable until after death.
Please note, you cannot waist your words talking nonsense, why, because this will be considered wasteful, now you are allowed to talk about work, relationships, and things along the line, though pointless chatter, gossip etc will get you in trouble.
As was pointed out by @Rabbi Kaii, the dress code should be according to Halacha, no not Black and white, just clean and modest, it could be a nice pair of jeans with a checkered shirt, or a polo, just nothing that goes in the ways of the goyim, or that draws to much attention, flamboyancy, you may dress classy, fancy if that's your regular code, though you may not start to dress to impress, or to show off, as this will be ga'ava and another form of degrading his name. So it's an intense, internal personal journey, that you should go through in my opinion, either way, you must be truthful with yourself and dress to beautify or enhance the name(presence that you will be in). Incase I need to state the obvious, the undergarments must be clean at all times, if your are going to sweat a lot, it would be best to withhold on the meditation (image) until when you are clean and if you would like to go through the day as such, you should hold it until you can find a way to resolve the excessive sweating throughout the day.
Hope this helps to answer your question, and not redirected you or left you unsatisfied.
Have a good day!