Question needs more information (such as the format of the input data etc.) as per my comment, but here's the basics of something functional:

#!/bin/bash

while IFS=',' read -r -a array ; do
  if [ -z "${array[1]}" ] ; then
    fc="NA"
  elif (( "${array[1]}" > 0 )); then
    fc=1
  elif (( "${array[1]}" < 0 )); then
    fc=0
  fi
  echo "${array[0]},$fc"
done < $1

Assuming an input file like:

$ cat test.csv
Gene1,1
Gene2,10
Gene3,
Gene4,-1
Gene5,-30

bash scriptname.sh test.csv will yield:

Gene1,1
Gene2,1
Gene3,NA
Gene4,0
Gene5,0

NOTE:

bash cannot do floating point arithmetic (unless you subprocess to bc or something), so if you have floating point data, this is why I would strongly urge the use of Python/R or something as per my comment also. Additionally this is why it's important to provide example input data.

Floating point calculations would require something like the following:

#!/bin/bash

while IFS=',' read -r -a array ; do
  if [ -z "${array[1]}" ] ; then
    fc="NA"
  elif (( $(echo "${array[1]} > 0" | bc)  )); then
    fc=1
  elif (( $(echo "${array[1]} < 0" | bc) )); then
    fc=0
  fi
  echo "${array[0]},$fc"
done < $1

Which for the input:

Gene1,1
Gene2,10
Gene3,
Gene4,-1
Gene5,-30
Gene6,1.234
Gene7,0.999999999999999999999999999999999
Gene8,-0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000001

will give:

Gene1,1
Gene2,1
Gene3,NA
Gene4,0
Gene5,0
Gene6,1
Gene7,1
Gene8,0

As a final comment, this will still not work for standard scientific notation for exponents (1E+10 etc.). In order for that to work with bc, the E would need to be substituted for a *10^ string.

$ echo -e "gene1 100.2\ngene2 -100.4\ngene3" | awk '{OFS="\t";V=($2==""?"NA":($2>=0?1:-1)); print $1,V;}' 
gene1   1
gene2   -1
gene3   NA