B727 CREW HAD RWY INCURSION AT NIGHT AT LAS.

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ACR FLT ABC REQUESTED TAXI FROM RAMP (PUSHED FROM GATE ABC). RECEIVED CLRNC TO TXWY S TO TXWY G TO TXWY W TO TXWY B TO BRAVO5. PROCEEDED ON TXWY S. ACFT HAD NO TAXI LIGHT. WE WERE LOOKING FOR TXWY G WHEN WE SAW THE RWY SIGN FOR RWY 19L. I APPLIED THE BRAKES AND STOPPED ABRUPTLY. WE GAVE RAMP A CALL AND INDICATED THAT WE MISSED TXWY G. THEY HAD US GIVE GND A CALL. WHEN WE GAVE GND A CALL; WE TOLD THEM WE WERE ON TXWY S SHORT OF THE RWY. GND GAVE US INSTRUCTIONS TO MAKE THE L TURN ONTO THE RWY AND MAKE THE FIRST AVAILABLE L TURN AND CONTINUE OUR TAXI TO RWY 25R. WE DID AS INSTRUCTED. THE INTXN OF TXWYS G AND S IS NOT MARKED WITH TXWY SIGNS. RAMP CTL SEEMS TO BE RUNNING PART OF GND CTL. THE ACFT DID NOT HAVE A TXWY LIGHT COMPOUNDING THE PROB. AS SOON AS WE SAW THE RWY SIGN; WE STOPPED AND ASKED QUESTIONS BEFORE PROCEEDING BLINDLY FORWARD. WE ALSO NOTICED MULTIPLE SIGNS MISSING AT MULTIPLE INTXNS AT LAS VEGAS. LAS VEGAS NEEDS BETTER COM AND HANDLING BTWN RAMP AND GND CTL. IN ADDITION; FOR ACFT WITHOUT TAXI LIGHTS OR SITS WHICH MIGHT REDUCE VISIBILITY; TXWY SIGNS BECOME IMPERATIVE AND ADD CONFUSION WHEN THERE ARE NONE.