A container seal that has been broken or tampered with does not necessarily mean a theft has taken place. It may simply mean that there has been a customs inspection. If this happens in the US, US customs will usually put on a new seal and mark it so you know it’s been opened by the US customs. They will also return you the original seal.
If there is no evidence of a broken seal due to customs inspection and unauthorized entry is suspected, you should document everything. Take photos of the seal (if any) and the container. Contact your carrier, freight forwarder, and insurance company immediately. Do not, however, open your container until a representative of the shipping line is present. Continue taking photos of the contents once the container has been opened. This is important in the event that you wish to file a claim against the carrier.
Container seals are not entry-proof
Container seals aren’t entry-proof and you shouldn’t rely on it 100% to prevent theft. Its main functions are to deter unauthorized entry and to determine if there’s been one by acting as evidence of tampering.
You may, however, opt for added measures for extra protection if you wish. These include using multiple seals with a variety of sizes, styles, colors, and most importantly, combinations. Other means such as warning labels can also be considered for extra precaution.