Evidence that the accused committed other similar forgeries about the same time of that charged, is competent to show criminal intent.256 And of course several forgeries may be shown in evidence where they form part of one and the same transaction, being part of the res gestae.257 But there must be strict proof that such other instruments are forgeries, otherwise it is error to permit them in evidence.258 And the burden is on the prosecution to prove such other alleged forgeries.259 And the same rule governs on the trial of a charge of having possession of or uttering an instrument alleged to be forged.260

On a charge of forgery evidence of uttering an instrument alleged to be forged is competent as tending to prove criminal intent.261