It is a bit more than just “blow”, I think (in fact, the query term is “breathe”, not “blow”). It seems to be a newly patented technology that has been designed to react by changing the colour and also showing the word “valid” when the user touches, rubs or breathes upon the seal. In the case of “breathing”, it is the heat from the breath (therefore the “vaho”) which brings about the reaction of the technology and displays the message. Being the heat from the breath, I believe, essential for the verification process, I would speak of “exhalar vaho”.


http://www.keyplusinc.com/html/securitytechnologies.html
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"Heat Reactive Verification Seal"
Touch or breathe on fingerprint area and a "valid" message will verify authenticity. This technology is one of the highest security features you can utilize. It is also laser compatible.