Believe it or not, it's actually called a seal.
The point of a seal is to close something and provide evidence that it's been subsequently opened. This happens with wax seals, with gummed envelopes, and it's the same here. Either the seal is torn, or layers within it separate so there is evidence that it was once stuck to the doorframe.
Here's an advertising image from a manufacturer (Biffar) showing it's what they call them:
Note that different seals might be identified differently. This one is labelled "Crime scene" so they promote it as "Crime Scene Seal". However premises might be sealed for any purpose, including (for example) by executors if the property is part of someone's estate after their death. The generic name is simply seal.