A C150 WITH A FLT INSTRUCTOR AND STUDENT ON BOARD WERE UNABLE TO SEE RWY SIGNS OR HOLD SHORT LINES AND TAXI ONTO A RWY WITH TFC ON FINAL.

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WE WERE CLRED TO TAXI FROM THE N RAMP AT BET TO RWY 29 VIA TXWY C. WE WERE INSTRUCTED TO USE THE R SIDE OF THE TXWY FOR 2-WAY TFC. BEING NEW TO THE ARPT; I WAS UNFAMILIAR WITH THE LAYOUT; AS WAS MY STUDENT; WHO WAS ON HIS 4TH LESSON. SINCE WE WERE TAXIING DIRECTLY INTO THE AFTERNOON SUN; WE WERE UNABLE TO READ ANY OF THE POS SIGNS AND WE FOUND THAT THE SURFACE MARKINGS WERE OBSCURED BY SNOW. AS WE WERE UNABLE TO READ ANY OF THE POS SIGNS AND WE FOUND THAT THE SURFACE MARKINGS WERE OBSCURED BY SNOW. AS WE TAXIED S; I LOOKED FOR THE THRESHOLD LIGHTS TO DETERMINE WHERE RWY 29 BEGAN. TO THE R; I SAW WHAT APPEARED TO BE THRESHOLD LIGHTS OFFSET TO EITHER SIDE OF THE RWY WITH THE TXWY LEADING UP BTWN THEM. WE TAXIED UP TO THIS POINT AND FOUND THAT IT WAS JUST A GROUPING OF TXWY LIGHTS AND THAT THE REAL THRESHOLD LIGHTS WERE BEHIND US. AT THAT POINT THE TWR ORDERED US TO VACATE THE RWY IMMEDIATELY AND WE DID SO. IT TURNS OUT ANOTHER ACFT WAS ON FINAL. SIGNS ON THE L SIDE OF THE TXWY WERE OBSCURED BY TFC MOVING IN THE OPPOSITE DIRECTION.