Up to a certain threshold, professionalism is a matter of perception and, what matter the most, of shared perception between you and the company.
What I mean with this? I mean that a company could think that the only way to be professional is wearing a tie, another one could think exactly the opposite, and there is no clear stats unless you work in some specific environments or countries.
I've seen in companies that didn't care at all about how good you were at your job, what did matter was the tie.
I've been a project manager and did interviews myself, and I discarded all people that presented with a tie or those that where totally freaking nerds 'cause it was a small company and the team was working with a certain kind of spirit.
I've met a guy who is running a hugely successful company in Milano and he hire only weird, crazy, nerd guys.
Every company has its targets and decided its way to reach them; at the same time, you as a human being have a standard of what you feel is comfortable for you and the environment you want to spend a lot of your time in.
So what you should be asking yourself is: "Will I look unprofessional in the context of the companies/countries I'm going to work, and do I really care to work with them? Is it acceptable for me to change myself to adapt to a certain company?"
You can put stickers on your laptop, knowing that some (rare, I think) companies could see it as unprofessional and will ask you to remove them, and you can just ignore those companies and choose the ones that are more in sync with you. Or you can mask yourself and not put stickers because you feel you want to work for that a company.
You can do whatever you want, as much as it makes you feel good! There's a ton of job out there to choose from, so choose what makes you happy.