Electronic – How to generate a -24V signal

Many lab supplies (Instek, GW Precision) have three output connections: positive, negative and earth. If you disconnect earth from negative, you 'float' the output and can easily use it as a negative supply (put the positive to your ground, and the negative will provide your -DC).

Edit - I realised you might want from 0V to +5V for -24V to 0V, so here is another NPN based option that might do the trick, and also does not need the -24V rail. I left the FET based circuit there anyway in case it is of interest. As noted below you might have to fiddle with values a bit, this was just intended to put the idea across.
I wasn't entirely sure whether the signal is analog or digital, as you mention digital in the title, but also an acquisition device (so I thought it may be possibly heading for an ADC) so I assumed either was possible, hence the attempt at linearity.

NPN circuit

NPN circuit simulation

Alternative Option

An N-channel FET source follower might work okay with a voltage divider on the input. Say something like a 10:1 divider for a range of -2.4V-0V at the gate. The source of the FET to 0V through a resistor and drain to +5V.
This won't be the most linear but shouldn't be too bad if you fiddle around with values a bit to adjust the desired ratios. You could maybe add a constant current source (e.g another N-channel FET with source to -24V through e.g a 5K resistor, gate tied to source and drain to source of upper FET) on the source to make it more linear if necessary.

Here is a circuit and simulation of the (more linear) constant current idea (the green line is +Vout as Vin is swept from -24V to 0V):

FET circuit

FET circuit simulation