Specifically so that wallets can't say exaggerations like this, a wallet security commitee needs to be formed.
Its members should include contributors to various open-source wallets, as well as security professionals working for the big wallet companies.
Their sole function would be to review the source code of every wallet (an audit) and then assign it a rating like A+, A, etc. It would also give out 0 ratings to wallets which aren't code-signed (not a problem as you can buy these from second-hand TLS sites for $60/year). In my opinion, all wallets should be code-signed by a reputable CA (even Electrum, eventually).
This could turn into a dangerous thing because there is always a chance that the centralized "committee" could get corrupted very easily. We saw this in other centralized authorities when money was involved for example the ICO benchmarks that all ended up advertising the biggest scams that paid them the most amount of money.