I am in the habit of often specifying the license on what I write, for many reasons. This license is usually The Creative Commons license CC BY-SA. It does not create any conflict with StackExchange because that is precisely the license that is needed for StackExchange as specified in the Terms of Service. So the operation of StackExchange can in no way be disrupted by such a license on a post.
There is nothing in the Terms of Service, or anywhere that I could see, that prohibits this.
I can understand that having a license on each little bit of information can be bothersome for users of the site, and is not very meaningful anyway. Hence I am refraining from using it on smaller pieces of writing. On a larger piece, it is small enough that it is hardly noticeable.
Why do I want to do it ?
The first reason is that a lot of people will copy a document without thinking further about copyright issues. They will usually keep the license if it is there, but will not bother when it is implicit. Given that I am using a pseudo, that quickly makes an orphan work with no license on the web, which some people could appropriate through specific legislations, and I do not want that. I have no certainty that anyone, other than myself or close relatives, will want and have the right in the future to preserve open access to what I write.
The second reason is educational. It is important in the digital world that people understand the existence of licenses, and their role. It is apparent to me that users of StackExchange do not. Licenses may protect the rights and income of authors in some cases, but they may also protect works and the right of all people to access and use them. That form of awareness is socially extremely important, and scientists should more than all others be aware of it as it is crucial for their work.
Should I remind the users of this community that the open access movement is nowadays championned by the academic world in general, and is supported by the best universities and research centers in the world (including several I worked for). In addition, its origins are to be traced to the physics community and the work of physicist Paul Ginsparg who created arXiv, the first open archive, at the Los Alamos National Laboratory.
This historical role of the physics community makes it all the more worrisome to find out that many of its current members do not understand the role and effect of the appropriate use of licenses.
The last reason is simply to say thank you to people like Lawrence Lessig and the whole Creative Commons community, and indirectly to Richard M. Stallman who invented the type of licenses now used in StackExchange and many other places to preserve everyone's access to knowledge, éducation and culture.
It is customary, and even required, in the academic community to give references to the works we have been using. We do use these licenses all the time, and our work owes them more and more. It seems only fitting to mention them regularly, without abusing it on minor contributions.
Why am I saying this ?
My remarks about the fact that many members of this community do not understand the meaning and role of licenses is based on the exchange of comments when I did include a license with one or two of my posts (I do spend significant time on some). One user went so far as to edit my post to remove the license, arguing that it was controversial.
Being controversial does not seem to me a sufficient reason to erase something. Controversy is an essential ingredient of creation and advancement of knowledge. Free speech was actually an academic creation, and some universities still maintain an age-old tradition of having (now symbolic) bodyguards for people defending their doctoral dissertation, so that they can speak freely. Free speech is supposed to be the rule, unless a clear problem can be identified, to say things as loosely as possible. This was just this user's opinion against mine, and though he may be a trusted user, that is obviously not his kind of expertise.
As a matter of fact, erasing a license or any kind of copyright information from a work is generally an offense punishable by law, probably in his country, certainly in mine, in the USA and in most countries in the world. I do not mean this as any kind of threat, but only as an example of general illiteracy in those matters, which actually justifies my position above, especially in regard to education. Actually he would have a good defense, the only possible one: this is the license demanded on this site, so that he was not really changing anything. But if that is the case, why erase it ? It obviously is not controversial.