Returning a viewmodel
Why not name them both the same? The difference is the type of parameter you're passing. This leaves you free to do some method overloading:

public SubscriptionsViewModel GetSubscriptionsViewModel(Guid id)
{
    //GET Logic here...
}

public SubscriptionsViewModel GetSubscriptionsViewModel(SubscriptionsViewModel viewModel)
{
    //POST Logic here...
}


Why call them the same? They both do the same: return a SubscriptionsViewModel.