On page 208-210 of The Rediscovery of the Mind, Searle writes:

On the standard textbook definition of computation, it is hard to see how to avoid the following results:

1. For any object there is some description of that object such that under that description the object is a digital computer.

2. For any program and for any sufficiently complex object, there is some description of the object under which it is implementing the program. Thus for example the wall behind my back is right now implementing the Wordstar program, because there is some pattern of molecule movements that is isomorphic with the formal structure of Wordstar. But if the wall is implementing Wordstar, then if it is a big enough wall it is implementing any program, including any program implemented in the brain. [...]

I do not think that the problem of universal realizability is a serious one. I think it is possible to block the result of universal realizability by tightening up our definition of computation. Certainly we ought to respect the fact that programmers and engineers regard it as a quirk of Turing's original definitions and not as a real feature of computation. Unpublished works by Brian Smith, Vinod Goel, and John Batali all suggest that a more realistic definition of computation will emphasize such features as the causal relations among program states, programmability and controllability of the mechanism, and situatedness in the real world. All these will produce the result that the pattern is not enough. There must be a causal structure sufficient to warrant counterfactuals. But these further restrictions on the definition of computation are no help in the present discussion because the really deep problem is that syntax is essentially an observer-relative notion. The multiple realizability of computationally equivalent processes in different physical media is not just a sign that the processes are abstract, but that they are not intrinsic to the system at all. They depend on an interpretation from outside. We were looking for some facts of the matter that would make brain processes computational; but given the way we have defined computation, there never could be any such facts of the matter. We can't, on the one hand, say that anything is a digital computer if we can assign a syntax to it, and then suppose there is a factual question intrinsic to its physical operation whether or not a natural system such as the brain is a digital computer.

And if the word "syntax" seems puzzling, the same point can be stated without it. That is, someone might claim that the notions of "syntax" and "symbols" are just a manner of speaking and that what we are really interested in is the existence of systems with discrete physical phenomena and state transitions between them. On this view, we don't really need 0's and l's; they are just a convenient shorthand. But, I believe, this move is no help. A physical state of a system is a computational state only relative to the assignment to that state of some computational role, function, or interpretation. The same problem arises without 0's and l's because notions such as computation, algorithm, and program do not name intrinsic physical features of systems. Computational states are not discovered within the physics, they are assigned to the physics.