I would like to listen to my own transmitted signal using a second receiver and connecting one into the other could possibly be a bad idea ;-) so How can I safely tap into my transmitted signal without risking melting the receiver?
If the receiver is close to the transmitter, and you are transmitting with more than a few milliwatts, just fire up the receiver with no antenna attached. Not having an antenna makes the receiver far less sensitive, but with the path loss being only some feet, it really doesn't need to be very sensitive.
Also, there's a lot of attenuators out there. Just do the math: If your transmitter is capable of thransmitting let's say 20 dBm, and your receiver has a sensitivity of -90 dBm and a max input of 10 dBm, then your maximum attenuation you could use is ( 20 - (-90) ) dB = 110 dB, and the mininimum necessary is ( 20 - 10 ) dB = 10 dB. Always go for the higher end, since attenuators are practically noise-free, and short output power spikes above what you're expecting could fry your receiver. 60 dB is a common value, so that's what I'd use here.
Phil's answer is also pretty perfect.
The point I want to stress here is that if you want to
safely tap into my transmitted signal without risking melting the receiver
you'll need the "melting point" (max. input power) of your receiver, and the amount of "heat" (max output power) of your transmitter. As Phil pointed out, it's pretty unlikely you'll fry your receiver without an antenna attached to its open port (which is, technically, still an antenna, because it's now the interface between the 50 or 75 $\Omega$ line impedance and free space impedance, but a bad antenna; think of it as miniature horn antenna), but that's just because the efficiency at which such ports pick up energy are pretty small.