Yes the directive 2006/42/EC seems to be a bit vague when it comes to buttons or UI in general. From the directive, chapter 1.2.2 Control devices:
- clearly visible and identifiable, using pictograms where appropriate
Yes, seems reasonable. But as @slyimperator said, icons can be culturally defined. I think that any CNC machinery made in Europe conforms with the directive, you could take a look at one of them?
Additionally Guide to application of the Machinery Directive 2006/42/EC expands this a bit. From §186 Identification of control devices (emphasis added):
The first indent of section 1.2.2 on the visibility and clear identification of control devices, aims to enable operators to use the devices without hesitation and avoid unintended commands due to operators confusing one control device with another. Since operators are often liable to perform different tasks and use several different machines in the course of their activity, it is important for manufacturers to identify control devices using, as far as possible, standardised colours, shapes and pictograms so that operators are not surprised when they change tasks or move from one machine to another. If the function of a control device is obvious from its standard shape and location such as, for example, a steering wheel or handlebars on mobile machinery, additional means of identification are not required.
If jogging an axis of the machine is something that can be hazardous to user then yes, action to do it must be designed so that it couldn't happen by accident, from the same chapter 1.2.2 Control devices:
designed or protected in such a way that the desired effect, where a hazard is involved, can only be achieved by a deliberate action
And from Guide to application of the Machinery Directive 2006/42/EC §190 Preventing inadvertent operation of control devices:
The requirement set out in the sixth indent of section 1.2.2 aims to avoid inadvertent operation of control devices. Inadvertent operation can result from various causes, such as, for example, accidental contact between a part of the operator's body or of his or her clothing and a control device, unintentional operation of two adjacent control devices (for example, pushing two buttons or levers with one hand or two pedals with one foot), a control device being caught on an obstacle in the environment of the machinery or use of a control device as a hand hold for access to the operating position[.]
To me this all reads like ISO 9241, especially ISO 9241-210.