UL (formerly Underwriters Laboratories) provide the Cybersecurity Assurance Program to certify that an Internet of Things device is, in their opinion, secure from most major threats.
UL seem to be highly respected in their certification processes, according to Ars Technica:
UL, the 122-year-old safety standards organisation whose various marks (UL, ENEC, etc.) certify minimum safety standards in fields as diverse as electrical wiring, cleaning products, and even dietary supplements, is now tackling the cybersecurity of Internet of Things (IoT) devices with its new UL 2900 certification.
UL describe their certification as involving:
- Fuzz testing of products to identify zero day
vulnerabilities over all interfaces
- Evaluation of known vulnerabilities on products that
have not been patched using the Common Vulnerability
Enumerations (CVE) scheme
- Identification of known malware on products
- Static source code analysis for software weaknesses
identified by Common Weakness Enumerations (CWE)
- Static binary analysis for software weaknesses identified
by Common Weakness Enumerations (CWE), open source
software and third party libraries
- Specific security controls identified for use in products
that reduce the security risk [...]
- Structured penetration testing of products based on flaws
identified in other tests
- Risk assessment of product security mitigation designed
However, the exact process in which UL scrutinise devices is unclear (unless you pay to buy the full set of specifications), as Ars Technica note (and criticise):
When Ars requested a copy of the UL 2900 docs to take a closer look at the standard, UL (formerly known as Underwriters Laboratories) declined, indicating that if we wished to purchase a copy—retail price, around £600/$800 for the full set—we were welcome to do so. Independent security researchers are also, we must assume, welcome to become UL retail customers.
Although UL are respected, we cannot assume that their certification is particularly sound in terms of security without further scrutiny, though it does satisfy the original question.
Unfortunately, I couldn't find any open standards/certifications for security, though this is likely because the resources required would be far too large for a non-profit association.