Clearly there is no pure system, which is what has lead to the phrase, "follow the spirit or the letter of the law." No legal or regulatory system can be perfect in execution. Usually rules lead to loopholes or quirks that can in sometimes undo the original purpose. But when met with fairly unambiguous language in a law that the administration wants to break, they had to create a fake loophole. The constitution and law has allowed some flexibility in legally stopping or knocking out congressional passed laws. There are three forms of vetoes: plain veto which can be overridden, pocket veto which cannot be overridden, but only works on end of session laws, and line item vetoes which are peculiar in usage, practice and legality. This administration has started using a fourth one which is bizarre: signing statements. A better term for this is the "cross your fingers" veto.
A signature is supposed to signify your acceptance of the assertion of the document. In the case of signing a bill as passed and delivered by Congress, the signing (or not signing in the middle of a congressional session) means the bill becomes law. After that point only the courts can overrule the law or another counteracting law can get passed. The current administration is under the delusion that it can counteract the force of the law by writing a statement that indicates the intention of the administration to follow or not follow the law.
This "crossing your fingers" is actually a positive development for this administration, because it helps us anticipate which laws the administration is planning to break. In a sense we can see the fingers being crossed while they sign the bill. Perhaps the courts should interpret this as an actual veto which can be overridden. There is an element of signing documents that depends on intent and the mental condition of the signer (for example, was it under duress).
The irony here is that the law that the president "crossed his fingers" while signing is the anti-torture law. Torture is often the means to get a confession and sometimes ones which is signed. Under current law, the signature is unenforceable. When the president signed the anti-torture bill into law, he was not being tortured or coerced into signing. But he used a similar out to disembowel the law to protect the lives of people.