Many companies offer broth in a box carton with a twist-off cap. In the US, these are usually 32 oz cartons but may be other sizes as well. Twisting the cap breaks a foil seal underneath, allowing one to pour the stock. There is no way to remove the cap without breaking the foil seal, meaning there is no way to know if the foil seal was intact before it was broken as part of opening the carton. There may be some external signs that the seal is not intact or the product is otherwise not fresh (leaking, bulging, etc), but how can I tell that the broth inside is safe to use? Larger cartons sometimes have a flip-open top and one must pull up the foil seal separately. Smaller containers are usually in cans. Neither have this problem. Example container from Swanson:  Image taken from Campbell's website 
After several edits to incorporate suggestions from comments [now gone] The thing to take away from this answer is that the seal itelf is not the primary indicator of tampering. Because there are many methods of exposing the seal, some of which will actually break the seal by the simple action of trying to check its integrity, then your indicator is the tamper-evident lid… not the seal itself.  In some designs…The lid when new is not fully closed [see above]. You must close it to puncture the foil seal using a 'blade' mechanism in the lid itself. This also breaks the plastic tamper-proof seal which is an integral part of the lid. There are variants on this design [see above] including ones that break the seal as you first unscrew the lid, but all have the tamper-evident lid & some mechanism to break the seal on first opening. This plastic tamper-proof device is your evidence the seal may be compromised. No other evidence can be known at this point. Even if someone just removed the lid, though they may not have broken the food seal, you could see they'd broken the plastic lid. You don't have to check for pressure or any other signs of spoilage, just look at the tamper device on the lid. The carton re-seals perfectly with the lid fully tightened by the consumer after purchase, so pressure, leakage etc is not the true sign is has been tampered with, merely additional tell-tales. The old method of having a separate pull-off seal underneath wasn't really liked by either consumer or manufacturer. For the consumer it meant a two-step process; those seals can be annoying if you don't have full mobility [& even if you do]. For the manufacturer, it meant they had to employ a secondary piece, manufactured & adhered separately; more room for error & more expensive. The new design means the seal is part of the inner box; card, foil, plastic. All they need to do is leave a hole in the card before laminating the rest. The lid protects it before sale & contains the mechanism to puncture it before use. Easier, cheaper, greener. Here's one major manufacturer's version of this lid design, TetraPak - https://www.tetrapak.com/en-us/solutions/packaging/packaging-material/helicap--23 Tamper-proof seal, unbroken  If broken, the ring where those small gaps are will be separated from the rest of the lid & loose. BTW, in the UK at least, even the flip-top containers now have this single 'open to puncture' mechanism. The flip top is a lever mechanism which itself penetrates the seal on first opening, then clips shut again. Except for bottled [as opposed to carton, UHT] milk, I think most of the old pull-top type seals are gone. 