|No such thing as a small change|
IANAL but my understanding of the relevant laws says that the author owns anything they write unless that default is superceded somehow (eg your contract with your employer). This is true whether or not you have a statement of copyright in the code. It is not within the power of PerlMonks to give permission on any code that appears here unless it owns that code. Transferring ownership would either require a contract between would-be authors and PerlMonks (which doesn't exist) or would require a lot of paperwork. Neither of which is likely to happen.
That is the bad news.
There is worse news. The odds are high that your employer owns copyright to all of the code that you write for them. Think about this carefully before posting stuff here out of code written for your job.
But it is not all bad. For instance did you know that violating someone else's copyright doesn't generally matter if they have no objections? All that a copyright license does is lays out conditions which are sufficient to get permission to do things otherwise prohibited by copyright law. However the copyright owner can choose to retroactively give you permission for anything they want. (Of course at that point they have you over a barrel and could try to extort whatever they want from you.) So if someone answers you with some code, while you may have no legal protection should you choose to use that, do you really think the author will object?
You see lawyers do a lot of worrying over what-ifs and might-bes. Legal contracts try to nail down the various ways in which people will and won't be nasty to each other. However many geeks take an attitude towards lawyers that can be summed up with, "If I ignore you long enough, will you go away?" As long as all parties are inclined to be reasonable, this works fairly well. Most geeks are inclined towards being reasonable. Of course if someone is out to make you miserable, that is a recipe for disaster.
So I would say that you should decide your own comfort level. I don't worry about 5 line snippets. If I want to use a longer piece of code, I will ask for permission. I have had people ask me for permission to use code. And I have been known to put a copyright statement on longer pieces of code.
Of course that isn't legal advice. That is just where my comfort level is. After all if someone sends you a message in chatter saying, "It is OK to use that, else I wouldn't have posted it" - are you protected in court? If they sued you, can you prove it was them who gave you the message? Perhaps you would prefer an email? Perhaps you want it in writing? If you are concerned, then you should talk to a lawyer to determine what level of protection you want.