Question
We were looking at slogans for tshirts and wanted to know how to find out if something is an infringement.
Answer
U.S. Copyright Office: http://www.copyright.gov/
Patents & Trademarks: http://www.uspto.gov/
Answer
Everything is copyrighted anymore, and explicit copyright notices are not required. Copyright notices are essentially just a reminder anymore, and perhaps provide a date of creation and info on the party to contact, should you wish to use their content in an otherwise restricted fashion. So unless something is marked as released to the public domain it is protected whether any notice is given or not.
For trademarks, those are a bit more particular and well defined. Usage is protected simply by marking it as such, trade marked - TM. For a trade mark to remain valid though, rights are given based on first use as well, who created it first, and must be proactively protected - if you allow others to use it and you don't do anything about it, you may lose that protection.
Registering a trade mark is just that, legally registering of your mark so that its on file with the government to provide an official record of it, after which you replace the TM with the circled "R" - but its not a requirement for protection. And basically, the same thing goes for recorded copyrights, you can place a copyright on record, but its not a requirement, nor are explicit copyright notices required anymore.
In any case, for copyright or TM violation, the penalties are quite stiff, but generally require a cease and desist and subsequent violation before any suit will be heard in court.
Every instance of use for a trade mark doesn't have to be marked as such either. For example, I can mention eDale Trading here without adding the TM notation because the TM is noted elsewhere here - in a relatively conspicous manner, and in instances where there is no implication of any such ownership or conflicting use/claimed or confusing identity.
Another interesting thing about trade marks is that if you see something used somewhere that isn't identified as a trade mark, you may be able to create a derivative, claim it as a trade mark, and then claim the original to be in violation of your mark - if adequate similarity and possible confusion can be demonstrated.
The value to be gained or the damage of abuse - is it worth protecting, and the uniqueness of any such content has a lot to do these decisions and its ability to stand up in court as well.
As for international protection, that's an area I'd like to learn more about.
Answer
Note: just having the ® or an © isn't enough at times. Protect your Tradename as well. And consider a Service Mark as well if you're going for the gusto...
And always keep in mind. You are your own best cop in town. It doesn't mean anything unless you have money to chase violators down, and that's presuming they have anything worth going after. The legal system has all become very weak in the last 20 years despite the high costs of applications and searches and protections.
It does help though with Vero on ebay, and is worth it there. Tradename is very important.
Answer
....sell a prototype on eBay and see if it is vero'd....